Tropical Storm Flossie

Tropical Depression Flossie Track 1100 Hours August 05, 2019
Tropical Depression Flossie Track 1100 Hours August 05, 2019

Tropical Storm Flossie Satellite 0500 Hours August 2 2019Tropical Storm Flossie – NWS Central Pacific Hurricane Center Honolulu HI 500 PM HST Mon Aug 05 2019

Vigorous deep convection (see Monday video below)  has been persistent through much of the day to the northeast of the cloud system center, which has become significantly elongated and poorly defined by several outflow boundaries. Recent analyses of satellite cloud drift winds suggest that the highly elongated cloud system center is lacking westerly winds that define a closed area of low pressure, and subjective Dvorak current intensity estimates were 25 kt from HFO and SAB, while JTWC deemed the system too weak to classify. Given these inputs and the presence of continued vertical wind shear of more than 30 kt, Flossie will be designated a post-tropical remnant low. The intensity will remain 30 kt, since an ASCAT-C pass earlier in the day detected winds this strong within the deep convection. While the cloud system center could arguably be a trough, a mean center location gives an initial motion of 300/10 kt.

Under relentless vertical wind shear, the remnant low will continue to degenerate as it passes near the main Hawaiian Islands. The westerly vertical wind shear will be maintained by a deep upper-level trough parked northwest of the Hawaiian Islands. This upper trough is also eroding the low- to the mid-level ridge that is steering Flossie. As a result, the remnant low will gradually turn toward the northwest tonight, then shift toward the north-northwest until dissipation on Wednesday. The track forecast was nudged to the right from the prior advisory and is near TVCN. All guidance shows weakening or little change in intensity until dissipation.

This is the last advisory on Flossie. Additional information on this system can be found in the High Seas Forecasts issued by the National Weather Service in Honolulu under AWIPS header HFOHSFNP and WMO header FZPN40 PHFO. Interests in the main Hawaiian Islands should refer to products issued by the National Weather Service in Honolulu for information on flooding and surf impacts.

FORECAST POSITIONS AND MAX WINDS

INIT  06/0300Z 20.8N 154.6W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 12H  06/1200Z 22.1N 155.8W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 24H  07/0000Z 24.0N 156.8W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 36H  07/1200Z 26.0N 157.4W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 48H  08/0000Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 500 AM HST Mon Aug 05, 2019

A few bursts of deep convection have developed well to the north of the low-level circulation center (LLCC) of Flossie early this morning. The LLCC itself has been exposed for nearly 24 hours however, due to strong west-southwesterly vertical wind shear, analyzed to be around 30 knots. The latest subjective Dvorak current intensity estimate from PHFO was 2.0 (30 knots). The Advanced Dvorak Technique (ADT) current intensity estimate was 1.5 (25 knots). The initial intensity for this advisory has been held at 30 knots. The initial motion has been set at 285/13 knots.

Flossie is expected to make a turn toward the northwest with a slight decrease in forward speed later today as it rounds the southwestern periphery of a large subtropical ridge to the distant northeast. This general motion is then expected to continue through dissipation late Tuesday or Tuesday night. The latest track guidance has shifted to the north, and as a result, the official forecast track was adjusted slightly to the north of the previous advisory. This will bring the center of Flossie or its remnant low, very close to the main Hawaiian Islands later today through Tuesday.

Strong westerly vertical wind shear of 30 to 40 knots will continue to affect Flossie over the next couple days, inhibiting any intensification or re-organization of the tropical cyclone. Although brief bursts of deep convection will likely continue during the next couple days, Flossie is expected to become a post-tropical remnant low later today, with dissipation expected late Tuesday or Tuesday night. The official intensity forecast remains closely in line with the latest statistical and dynamical guidance.

Interests in the main Hawaiian Islands should refer to products issued by the National Weather Service in Honolulu for information on flooding and surf impacts from Tropical Depression Flossie.

FORECAST POSITIONS AND MAX WINDS
 
INIT  05/1500Z 19.7N 152.7W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 12H  06/0000Z 20.3N 154.4W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 24H  06/1200Z 21.5N 156.1W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 36H  07/0000Z 22.9N 157.7W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 48H  07/1200Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 1100 PM HST Sun Aug 04 2019

The low-level circulation center (LLCC) of Flossie (has been devoid of deep convection since around 1800 UTC, due to strong westerly vertical wind shear, analyzed to be around 30 knots. The latest subjective Dvorak current intensity estimate from PHFO was 2.0 (30 knots), while the system was deemed too weak to classify by SAB and JTWC. The Advanced Dvorak Technique (ADT) current intensity estimate was 1.5 (25 knots). The initial intensity for this advisory has been held, perhaps generously, at 30 knots. The initial motion has been set at 285/13 knots.

The west-northwest motion will continue tonight, with a turn toward the northwest and a slight decrease in forward speed expected Monday and Monday night as Flossie rounds the southwestern periphery of a large subtropical ridge to the distant northeast. The latest track guidance has shifted to the north, and as a result, the official forecast track was adjusted slightly to the north of the previous advisory. This will bring the center of Flossie or its remnant low, very close to the main Hawaiian Islands Monday through Tuesday.

Strong westerly vertical wind shear of 30 to 40 knots will lead to continued weakening of Flossie over the next couple days. Flossie is expected to remain a tropical depression tonight, before weakening into a post-tropical remnant low on Monday. The remnant low is then forecast to dissipate on Tuesday. The official intensity forecast remains closely in line with the latest statistical and dynamical guidance. Interests in the main Hawaiian Islands should refer to products issued by the National Weather Service in Honolulu for information on flooding and surf impacts from Tropical Depression Flossie.

FORECAST POSITIONS AND MAX WINDS

INIT  05/0900Z 19.4N 151.3W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 12H  05/1800Z 19.8N 153.2W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 24H  06/0600Z 20.8N 155.5W   25 KT  30 MPH - Tropical Depression (WSW Hilo, Hawaii)
 36H  06/1800Z 22.0N 157.0W   25 KT  30 MPH - Tropical Depression (WSW Hilo, Hawaii)
 48H  07/0600Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 500 AM HST Sun Aug 04 2019

Strong thunderstorms in Flossie’s eastern semicircle persisted for the first half of the night, prevented from moving over the low- level circulation center (LLCC) by persistent westerly vertical wind shear near 25 kt. Those thunderstorms began diminishing shortly after midnight, and while the LLCC remains obscured by mid- and high-level cloudiness, it appears poised to make an appearance. Subjective and objective Dvorak intensity estimates indicate that Flossie is barely hanging on as a tropical storm, and with the LLCC becoming increasingly exposed, the initial intensity estimate for this advisory is lowered to 35 kt.

Without any overnight microwave passes to assist with a center- finding, the initial motion estimate is primarily based on tracking what can be seen of the LLCC, yielding 280/11 kt. A low- to mid- level ridge north of the cyclone is expected to support a general motion toward the west over the next 24-36 hours, especially as Flossie weakens further and is steered by the low-level trade wind flow. After that, Flossie will round the western portion of the ridge, interact with a persistent deep-layer trough northwest of Hawaii, and dissipate. The updated track forecast was changed little from the previous, which represented a significant westward shift, and lies close to the EMXI and HCCA. Given average forecast error, a Tropical Storm Watch may be required for portions of the Hawaiian Islands later today.

The gradual spin-down of Flossie is expected to continue as it draws closer to the Hawaiian Islands, despite SSTs gradually warming to near 27C. The forecast track takes Flossie into an area of even greater vertical wind shear, leading to steady weakening, soon followed by dissipation.

FORECAST POSITIONS AND MAX WINDS

INIT  04/1500Z 19.3N 147.8W   35 KT  40 MPH - Tropical Storm (WSW Hilo, Hawaii)
 12H  05/0000Z 19.4N 149.7W   35 KT  40 MPH - Tropical Storm (WSW Hilo, Hawaii)
 24H  05/1200Z 19.7N 152.2W   35 KT  40 MPH - Tropical Storm (WSW Hilo, Hawaii)
 36H  06/0000Z 20.4N 154.8W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 48H  06/1200Z 21.6N 156.9W   25 KT  30 MPH - Tropical Depression (WSW Hilo, Hawaii)
 72H  07/1200Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 1100 PM HST Sat Aug 03 2019

Flossie’s satellite presentation is typical of a sheared tropical cyclone, with deep convection removed from the low level circulation center (LLCC). In this case, westerly vertical wind shear around 25 kt is keeping the convection displaced east of the LLCC, which remains obscured by mid- and high-level clouds. The initial intensity has been maintained at 40 kt for this advisory, as the satellite appearance has changed little since an earlier ASCAT pass indicating winds close to 40 kt, entirely in the northern semicircle. This is higher than the Dvorak intensity estimates that range from 1.0/25 kt to 2.5/35 kt from HFO/SAB/PGTW, but close to UW-CIMSS SATCON.

Flossie is tracking almost due west this evening, with an initial motion estimate of 280/11 kt. A low- to mid-level ridge north of Flossie has been supporting this motion for the past couple of days, and forecast models are now indicating that this ridge will remain stronger than originally anticipated in the short term. Track guidance has once again shifted to the left in response, and the official forecast follows suit, building on a trend that started about 24 hours ago.

HWRF/HMON and CTCI have been on the left side of the guidance envelope for several runs, taking Flossie very close to, or over, portions of the Hawaiian Islands Monday and Tuesday – albeit as a weak tropical cyclone. Other reliable models are now indicating a similar scenario, and the updated official forecast brings the center of Flossie over waters just east of the Hawaiian Islands as a tropical depression. Given recent trends and average forecast error, a Tropical Storm Watch may be required for portions of the Hawaiian Islands on Sunday. The updated track forecast closely follows the ECMWF guidance, and indicates a turn toward the northwest after 48 hours as Flossie finally rounds the ridge, and gets wrapped in the flow around a persistent deep-layer trough northwest of Hawaii.

The gradual spin down of Flossie is expected to continue as it draws closer to the Hawaiian Islands, despite SSTs gradually warming to near 27C. Vertical wind shear is expected to increase to over 30 kt after 24 hours, leading to steady weakening, and eventually dissipation. The intensity forecast is mainly an update of the prior forecast, and is close to the trends indicated by both the statistical and dynamical guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  04/0900Z 19.1N 146.7W   40 KT  45 MPH - Tropical Storm (WSW Hilo, Hawaii)
 12H  04/1800Z 19.3N 148.4W   35 KT  40 MPH - Tropical Storm (WSW Hilo, Hawaii)
 24H  05/0600Z 19.4N 150.8W   35 KT  40 MPH - Tropical Storm (WSW Hilo, Hawaii)
 36H  05/1800Z 19.9N 153.5W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 48H  06/0600Z 21.0N 155.9W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 72H  07/0600Z 22.9N 159.8W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  08/0600Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 500 AM HST Sat Aug 03, 2019

Flossie doesn’t have the most impressive satellite signature this morning, but deep convection continues to develop close to where the low-level circulation center (LLCC) is suspected to be. Subjective and objective Dvorak intensity estimates have changed little, and range from 2.0 to 3.0, with an average of the estimates from PHFO/SAB/PGTW/UW-CIMSS yielding an intensity estimate of 35-40 kt at best. However, there has been little overall change in the satellite appearance since the last advisory, when an ASCAT pass indicated 50 kt in the northern semicircle around 07Z. With that data in mind, the initial intensity estimate remains 50 kt.

Finding and tracking Flossie’s obscured LLCC remains a challenge, but it is estimated to be on the western edge of the deep convection, supported by a timely 1050Z GCOM pass. The initial motion estimate for this advisory is 285/12 kt, which represents a slowing in forward speed over the past 24 hours. Flossie is expected to move toward the west-northwest over the next 48 hours, steered by a low- to mid-level ridge centered to the north. On days 3 and 4, Flossie will round the western edge of the ridge, and Flossie will turn toward the northwest, with a slowing in forward speed. Model spread increases at that time, as is typically the case with recurving cyclones. The HWRF/HMON and COAMPS-TC indicate a track closer to the Hawaiian islands on the left side of the guidance envelope, while ECMWF and it’s ensemble mean are on the right side of the envelope.

Although the official forecast leans toward the high-performing ECMWF, it was nudged southward in the short term toward the HCCA, with the later forecast periods essentially an update of the previous track forecast. Although the environment in which Flossie is currently embedded is not conducive for a hurricane, it is marginally supportive of a tropical storm. Low- to mid-level easterly flow and relatively light winds aloft are allowing the LLCC to remain in relative proximity to the deep convection, despite vertical wind shear values near 20 kt. In about 36-48 hours, Flossie will arrive in an area where westerly vertical wind shear increases to 30-40 kt, and this unrelenting shear will lead to the demise of Flossie, especially as it moves over cooler water in the later forecast periods. The official forecast closely follows trends presented by SHIPS and the intensity consensus IVCN, with dissipation expected by the end of the forecast period.

FORECAST POSITIONS AND MAX WINDS

INIT  03/1500Z 18.6N 143.5W   50 KT  60 MPH - Tropical Storm (WSW Hilo, Hawaii)
 12H  04/0000Z 19.0N 145.3W   45 KT  50 MPH - Tropical Storm (WSW Hilo, Hawaii)
 24H  04/1200Z 19.5N 147.8W   40 KT  45 MPH - Tropical Storm (WSW Hilo, Hawaii)
 36H  05/0000Z 19.8N 150.1W   35 KT  40 MPH - Tropical Storm (WSW Hilo, Hawaii)
 48H  05/1200Z 20.4N 152.3W   35 KT  40 MPH - Tropical Storm (WSW Hilo, Hawaii)
 72H  06/1200Z 23.4N 155.8W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 96H  07/1200Z 26.0N 157.5W   25 KT  30 MPH - Tropical Depression (WSW Hilo, Hawaii)
120H  08/1200Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 1100 PM HST Fri Aug 02 2019

Despite Dvorak intensity estimates indicating that Flossie might be a tad weaker, and a somewhat unimpressive satellite appearance, the initial intensity estimate for this advisory was kept at 50 kt. Those winds are primarily located in the northern semicircle, where the gradient between Flossie and a low- to mid-level ridge to the north remains tight. A recently received ASCAT pass confirms this initial intensity, with a few 50 kt wind barbs noted in the northern semicircle.

Finding and tracking Flossie’s LLCC is difficult as it is obscured by mid- and high-level clouds, and the initial motion estimate is a somewhat uncertain 290/15 kt. The LLCC is estimated to be southwest of the deep convection, due to westerly vertical wind shear on the order of 20 to 25 kt. Several microwave passes were received between 02Z and 06Z, helping to locate the LLCC. The track forecast anticipates Flossie moving toward the west-northwest over the next day or two, with a slight reduction in forward speed, steered by the aforementioned ridge to the north. On days 3 and 4, Flossie will round the western edge of the ridge, and a turn toward the northwest is expected, with an additional slowing in forward speed. The updated track forecast is to the left of the previous due to a westward shift in most of the guidance, with FSSE and CTCI now joining the HWRF/HMON on the left side of the envelope. The updated track forecast lies close to the ECMWF guidance, which has been the best performer with Flossie.

Flossie is expected to traverse over marginal SSTs through most of the forecast period, with cooler SSTs expected by day 5 as it gains latitude. Furthermore, vertical shear is expected to increase to above 30 knots after 48 hours, although a slight reduction is possible in the short term. Given these factors, statistical and dynamical intensity guidance depicts only gradual weakening in the short term, with a greater rate of weakening thereafter. The intensity forecast was changed little from the previous, but now indicates Flossie becoming a post-tropical remnant low on days 4 and 5, with dissipation expected soon thereafter.

FORECAST POSITIONS AND MAX WINDS

INIT  03/0900Z 18.3N 142.3W   50 KT  60 MPH - Tropical Storm (WSW Hilo, Hawaii)
 12H  03/1800Z 18.9N 144.4W   45 KT  50 MPH - Tropical Storm (WSW Hilo, Hawaii)
 24H  04/0600Z 19.5N 146.5W   45 KT  50 MPH - Tropical Storm (WSW Hilo, Hawaii)
 36H  04/1800Z 19.8N 148.9W   40 KT  45 MPH - Tropical Storm (WSW Hilo, Hawaii)
 48H  05/0600Z 20.5N 151.3W   35 KT  40 MPH - Tropical Storm (WSW Hilo, Hawaii)
 72H  06/0600Z 22.7N 155.4W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
 96H  07/0600Z 25.6N 157.5W   25 KT  30 MPH - Tropical Depression (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 500 AM HST Fri Aug 02, 2019

Recent long- and short- wave infrared satellite images show that tropical storm Flossie  is a little more symmetric than it was last night. The center of the tropical storm appears to be more embedded within its central dense overcast. That said, the Dvorak Final-T and CI numbers from TAFB and SAB have not changed since 6 hours ago. Scatterometer data from earlier this morning supported max winds of about 60 kt, and this is agrees with the Dvorak fixes from TAFB and SAB, so the initial intensity remains at that value.

The track forecast has not been significantly changed from the previous advisory. Flossie continues to move west-northwestward, now at about 15 kt, and a subtropical ridge to the north should keep Flossie on this general heading for another 2 or 3 days. Most of the models suggest that Flossie will slow down slightly and then turn northwestward early next week, ahead of an upper-level trough located northwest of the Hawaiian Islands. By day 4, a turn toward the north is forecast by all of the typically reliable global models. The NHC forecast follows suit, showing recurvature east of Hawaii, and is very close to the HCCA and TVCE models at all forecast hours.

All of the intensity guidance forecasts that Flossie will gradually weaken over the next 3 to 4 days. The cyclone is moving over marginal sea surface temperatures near 26 deg C, and moderate shear of around 20 kt should continue to affect the cyclone through early next week. By 72 h, a sharp increase in westerly shear should occur as Flossie approaches the aforementioned upper-level trough, and additional weakening is anticipated.

The NHC intensity forecast is very similar to the previous one, and is near the middle of the low-spread intensity guidance envelope. On the forecast track, Flossie will move into the Central Pacific basin later today, at which point the Central Pacific Hurricane Center will assume forecast responsibilities.

FORECAST POSITIONS AND MAX WINDS

INIT  02/1500Z 17.1N 137.8W   60 KT  70 MPH - Tropical Storm (WSW Hilo, Hawaii)
 12H  03/0000Z 17.6N 140.1W   60 KT  70 MPH - Tropical Storm (WSW Hilo, Hawaii)
 24H  03/1200Z 18.3N 142.9W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 36H  04/0000Z 18.9N 145.4W   50 KT  60 MPH - Tropical Storm (WSW Hilo, Hawaii)
 48H  04/1200Z 19.3N 147.6W   45 KT  50 MPH - Tropical Storm (WSW Hilo, Hawaii)
 72H  05/1200Z 20.9N 152.2W   35 KT  40 MPH - Tropical Storm (WSW Hilo, Hawaii)
 96H  06/1200Z 24.5N 155.5W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)
120H  07/1200Z 29.0N 155.5W   30 KT  35 MPH - Tropical Depression (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 1100 PM HST Thu Aug 01 2019

An 0646 UTC ASCAT-B overpass captured Flossie’s entire tropical-storm-force wind field and confirmed that the structure remains asymmetric. Combining the scatterometer data and conventional infrared satellite images shows that Flossie’s center is embedded just within the southwestern edge of -70 degree Celsius cloud tops. The initial intensity remains 60 kt, which is a blend of Dvorak CI numbers from TAFB and SAB, and just above the 55 kt shown by the ASCAT data (accounting for possible undersampling).

Flossie just won’t slow down, as the initial motion is still west-northwestward or 285/16 kt. The subtropical ridge to the north remains strong, and this should keep Flossie on the west- northwestward trajectory for the next 3 days, although the track models insist that the current speed should decrease a bit. After day 3, a deepening upper-level low north and northwest of the Hawaiian Islands should cause Flossie to turn northwestward and then northward on days 4 and 5. The NHC official forecast depicts such a scenario, but this is where the forecast has the most uncertainty. All of the global models and most of the consensus models show Flossie recurving northeast of the Hawaiian Islands, while the regional HWRF and HMON models, as well as the Florida State Superensemble, are depicting a more southern solution with less recurvature. Despite these southern solutions, the new NHC forecast is relatively unchanged from the previous one and is very close to the HCCA and TVCX consensus aids.

Nearly steady shear of 15 kt and ocean temperatures around 27 degrees Celsius should keep Flossie’s intensity relatively steady for the next 12 hours or so. After that time, deep-layer shear is expected to steadily increase to at least 30 kt by 48 hours while Flossie also moves over a relative minimum in sea surface temperatures just under 26 degrees Celsius. These factors are likely to contribute to steady weakening, and there is relatively little spread among the intensity models in showing this scenario. The updated NHC intensity forecast has been lowered slightly from the previous one and shows Flossie becoming a tropical depression in 4 days.

On the forecast track, Flossie will be moving into the central Pacific basin in 12-24 hours, at which point the Central Pacific Hurricane Center will assume forecast responsibilities. In the meantime, users should continue to consult local forecasts from the National Weather Service Forecast Office in Honolulu, Hawaii, at www.weather.gov/hfo for information specific to the Hawaiian Islands.

FORECAST POSITIONS AND MAX WINDS

INIT  02/0900Z 16.8N 136.4W   60 KT  70 MPH - Tropical Storm (WSW Hilo, Hawaii)
 12H  02/1800Z 17.2N 138.7W   60 KT  70 MPH - Tropical Storm (ESE Hilo, Hawaii)
 24H  03/0600Z 17.9N 141.7W   55 KT  65 MPH - Tropical Storm (ESE Hilo, Hawaii)
 36H  03/1800Z 18.5N 144.3W   50 KT  60 MPH - Tropical Storm (ESE Hilo, Hawaii)
 48H  04/0600Z 19.0N 146.6W   45 KT  50 MPH - Tropical Storm (ESE Hilo, Hawaii)
 72H  05/0600Z 20.3N 151.3W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
 96H  06/0600Z 23.5N 155.0W   30 KT  35 MPH - Tropical Depression (ESE Hilo, Hawaii)
120H  07/0600Z 28.0N 156.0W   30 KT  35 MPH - Tropical Depression (ESE Hilo, Hawaii)

Tropical Storm Flossie NWS National Hurricane Center Miami FL 500 AM HST Thu Aug 01 2019

The structure of Flossie hasn’t changed in any meaningful way since last night. Recent SSMI microwave data indicate that the center of the tropical storm is displaced to the northwest of all of its deep convection, and its IR presentation hasn’t changed since the last advisory. Since Flossie’s appearance and structure has been nearly steady-state, the initial intensity remains 55 kt, based primarily on earlier ASCAT data.

The NHC intensity forecast is very similar to the previous advisory, and Flossie is still expected to remain a tropical storm for the next 5 days. The intensity guidance is finally in good agreement on the forecast, and all of the models indicate that that Flossie’s strength will not change substantially for the next day or two, followed by gradual weakening through early next week. In fact, the GFS now forecasts that Flossie will dissipate in about 5 days. The new official intensity forecast is near the middle of the intensity guidance envelope and is very close to IVCN at all forecast hours.

The initial motion of the cyclone is still 285/14 kt. There is high confidence in the first 72 h the track forecast, and all of the guidance continues to keep Flossie near its current heading and speed through that period. The spread increases dramatically after that, with the regional models (HWRF, HMON, COAMPS-TC) all taking a weak Flossie farther south, possibly even south of Hawaii, while the global models all show Flossie recurving east of the islands ahead of a mid- to upper-level trough. For the moment, the NHC forecast continues to favor the global model solution and does not show a significant change to the track forecast, however, it has been tweaked slightly southward at days 4 and 5.

It is worth noting that the confidence in the 5-day forecast position of Flossie is quite low, and the average error of track and intensity forecasts at that range is about 200 miles and 20 mph, respectively. In addition, hazards associated with tropical storms extend well away from the center of circulation. Users should therefore consult local forecasts from the National Weather Service Forecast Office in Honolulu, Hawaii, at www.weather.gov/hfo for information specific to the Hawaiian Islands.

FORECAST POSITIONS AND MAX WINDS

INIT  01/1500Z 15.1N 131.6W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 12H  02/0000Z 15.6N 133.9W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 24H  02/1200Z 16.3N 136.9W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 36H  03/0000Z 16.9N 139.8W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 48H  03/1200Z 17.5N 142.5W   50 KT  60 MPH - Tropical Storm (WSW Hilo, Hawaii)
 72H  04/1200Z 18.4N 147.5W   45 KT  50 MPH - Tropical Storm (WSW Hilo, Hawaii)
 96H  05/1200Z 19.5N 152.5W   45 KT  50 MPH - Tropical Storm (WSW Hilo, Hawaii)
120H  06/1200Z 22.5N 155.5W   35 KT  40 MPH - Tropical Storm (WSW Hilo, Hawaii)

 

NWS National Hurricane Center Miami FL 1100 PM HST Wed Jul 31, 2019

An ASCAT-B overpass from 0527 UTC was helpful in locating Flossie’s center and diagnosing the still-asymmetric wind field. At the time, the center was located beneath very cold cloud tops of -76 degrees Celsius, but that convection has since faded away due to the result of ongoing north-northwesterly shear. Dvorak Current Intensity numbers, SATCON, and the scatterometer data all support maintaining the 55-kt initial intensity.

Restrengthening of Flossie is no longer expected. For the next 3 days, mid-level shear below the outflow layer is likely to continue disrupting the vortex, and sea surface temperatures will be gradually falling by about a degree. This probably means the cyclone will continue producing bursts of deep convection that favor the eastern side of the circulation. Just about every intensity model either holds a steady intensity or shows slow weakening during the next few days, with the Florida State Superensemble the only model really showing any re-intensification (and it’s only 5 kt, at that). The new NHC intensity forecast, therefore, holds Flossie’s 55-kt intensity through 72 hours, which still ends up being higher than the model consensus. On days 4 and 5, Flossie runs into the teeth of deeper-layer westerly shear near the Hawaiian Islands, which is likely to cause weakening, if it hasn’t started already.

Flossie has taken on a more west-northwestward trajectory, with an initial motion of 285/14 kt. Mid-level ridging to the north of the cyclone is expected to be stationary but weaken, which should cause this heading to persist for the next 4 days with some reduction in speed. By the end of the forecast period, a deep-layer trough north of the Hawaiian Islands will influence the steering flow, causing Flossie to turn northwestward on day 5. The overall guidance envelope has shifted slightly northward, thus the new NHC track forecast is a little north of the previous forecast, most in line with the HCCA guidance and the TVCX model consensus.

Although models have trended toward a track just north of the Hawaiian Islands, we want to remind users that 5-day forecast positions and intensities have average errors of about 200 miles and 20 mph, respectively. In addition, hazards associated with tropical storms extend well away from the center of circulation. Users should, therefore, consult local forecasts from the National Weather Service Forecast Office in Honolulu, Hawaii, at www.weather.gov/hfo for information specific to the Hawaiian Islands.

FORECAST POSITIONS AND MAX WINDS

INIT  01/0900Z 14.7N 130.2W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 12H  01/1800Z 15.3N 132.5W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 24H  02/0600Z 16.0N 135.5W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 36H  02/1800Z 16.7N 138.5W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 48H  03/0600Z 17.4N 141.3W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 72H  04/0600Z 18.5N 146.3W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 96H  05/0600Z 19.5N 151.0W   50 KT  60 MPH - Tropical Storm (WSW Hilo, Hawaii)
120H  06/0600Z 22.0N 155.0W   40 KT  45 MPH - Tropical Storm (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 500 PM HST Wed Jul 31, 2019

Flossie is struggling this evening, with almost all of its deep convection in the southeastern quadrant of the circulation. While some thunderstorms have recently formed closer to the low-level center, the bursts have not been able to maintain themselves due to northwesterly shear. Satellite intensity estimates are a consensus 55 kt, so that will be the initial wind speed.

The intensity forecast, as usual, is challenging this evening. Shear is predicted to remain moderate/strong overnight, so some weakening is shown then. Afterward, while the upper-level wind pattern looks like it will become more conducive for strengthening through Saturday, the mid-level flow could keep the storm in a higher shear environment than would be expected from only a simple 850-200 mb shear calculation. Intensity models are also lower than the last cycle; however, a few of the models make Flossie a hurricane again. This isn’t a particularly confident scenario, so it is usually wise to be conservative when changing the forecast. Thus, the wind speed forecast is only about 5 kt lower than the previous one through 72 hours. The new NHC forecast is still higher than the model consensus, especially at long range, and further downward reductions are possible overnight if trends continue.

The storm continues to move westward at 14 kt, steered by a deep-layer ridge that stretches across much of the eastern Pacific. This ridge should steer Flossie westward to west-northwestward during the next several days. Model guidance shows less of a reduction in forward speed during the next 5 days than the last cycle, perhaps due to the now-weaker cyclone being more steered by the lower-level flow. Thus the new forecast is faster than the previous one, but lies basically along the previous NHC track. There is considerable uncertainty in the 5-day position and intensity, with average errors near 200 miles and 20 mph, respectively, so it’s best not to focus on specifics at that range.

FORECAST POSITIONS AND MAX WINDS

INIT  01/0300Z 14.3N 128.8W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 12H  01/1200Z 14.7N 131.0W   50 KT  60 MPH - Tropical Storm (WSW Hilo, Hawaii)
 24H  02/0000Z 15.4N 133.9W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 36H  02/1200Z 16.0N 136.8W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 48H  03/0000Z 16.6N 139.7W   60 KT  70 MPH - Tropical Storm (WSW Hilo, Hawaii)
 72H  04/0000Z 17.7N 145.1W   65 KT  75 MPH - Category 1 (WSW Hilo, Hawaii)
 96H  05/0000Z 18.5N 150.1W   60 KT  70 MPH - Tropical Storm (WSW Hilo, Hawaii)
120H  06/0000Z 20.0N 154.5W   45 KT  50 MPH - Tropical Storm (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 1100 AM HST Wed Jul 31, 2019

Satellite imagery indicates that Flossie  is weakening. The low-level center is now clearly exposed to the west of the main area of deep convection due to northwesterly wind shear. The objective and subjective intensity estimates have been decreasing, and the initial intensity is lowered to 60 kt based on an average of these data. This makes Flossie a tropical storm once again. Very recent ASCAT data also supports this downgrade.

Flossie is moving westward at 14 kt, steered by a deep-layer ridge that stretches across much of the eastern Pacific. This ridge is expected to remain in place and should steer Flossie westward to west-northwestward during the next several days. The track models are tightly clustered, and the NHC forecast lies near the usually reliable consensus aids. This forecast is slightly faster than the previous one, and brings Flossie into the Central Pacific basin in 2-3 days and near the Hawaiian Islands by the end of the forecast period.

The recent weakening of Flossie has been surprising since the shear was not expected to be as strong as observed. The poor current structure and the ongoing shear suggests that some additional weakening is likely in the short term. However, after that time, the global models show a more favorable upper-level wind pattern and, since SSTs are expected to remain sufficiently warm, some re-strengthening seems likely between 24 and 96 hours. Weakening is forecast by the end of the period due to another increase in shear. The NHC intensity forecast is a little lower than the previous one and lies near the IVCN and HCCA models. However, this intensity forecast is of lower confidence than normal.

FORECAST POSITIONS AND MAX WINDS

INIT  31/2100Z 14.0N 127.3W   60 KT  70 MPH - Tropical Storm (WSW Hilo, Hawaii)
 12H  01/0600Z 14.5N 129.4W   55 KT  65 MPH - Tropical Storm (WSW Hilo, Hawaii)
 24H  01/1800Z 15.1N 132.1W   60 KT  70 MPH - Tropical Storm (WSW Hilo, Hawaii)
 36H  02/0600Z 15.7N 135.0W   60 KT  70 MPH - Tropical Storm (WSW Hilo, Hawaii)
 48H  02/1800Z 16.3N 137.7W   65 KT  75 MPH - Category 1 (WSW Hilo, Hawaii)
 72H  03/1800Z 17.2N 143.2W   70 KT  80 MPH - Category 1 (WSW Hilo, Hawaii)
 96H  04/1800Z 18.0N 148.0W   70 KT  80 MPH - Category 1 (WSW Hilo, Hawaii)
120H  05/1800Z 19.3N 152.7W   60 KT  70 MPH - Tropical Storm (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 500 AM HST Wed Jul 31,2019

Flossie has the structure of a strongly sheared cyclone. Several recent microwave passes have revealed that Flossie’s center is displaced to the northwest of all of its deep convection, and IR imagery shows a sharp cloud-top temperature gradient in the northwest quadrant of the hurricane. A blend of Final-T and CI numbers from TAFB and SAB is the basis for the initial intensity of 65 kt, however, it is certainly possible that Flossie is weaker than that.

Given the current structure of Flossie (or lack thereof), a substantial change was made to the intensity forecast. The global models indicate that the current shear affecting the cyclone will likely continue for another 24 h or so and Flossie is now forecast to become a tropical storm during that time. In fact, the statistical guidance suggests that Flossie will merely gradually weaken for the next 5 days. On the other hand, the GFS, ECMWF, and regional hurricane models indicate that the upper-level environment could become more favorable in a few days, so some re-intensification is possible at that time. The NHC forecast now closely follows the intensity consensus through 48 h and then blends back toward the previous forecast at 72 h and beyond, still favoring the dynamical models at that time.

On the other hand, very little adjustment was required to the track forecast. The initial motion is 285/13 kt, and a persistent mid-level ridge to the north should keep Flossie moving west-northwestward or westward at a steady forward speed for the next 4 to 5 days. The track guidance remains very tightly clustered, and the NHC forecast is very close the typically reliable TVCE and HCCA aids.

FORECAST POSITIONS AND MAX WINDS

INIT  31/1500Z 14.0N 125.8W   65 KT  75 MPH - Category 1 (WSW Hilo, Hawaii)
 12H  01/0000Z 14.5N 127.7W   60 KT  70 MPH - Tropical Storm  (WSW Hilo, Hawaii)
 24H  01/1200Z 15.2N 130.3W   60 KT  70 MPH - Tropical Storm (WSW Hilo, Hawaii)
 36H  02/0000Z 15.8N 133.0W   65 KT  75 MPH - Category 1 (WSW Hilo, Hawaii)
 48H  02/1200Z 16.2N 135.7W   65 KT  75 MPH - Category 1 (WSW Hilo, Hawaii)
 72H  03/1200Z 17.2N 141.3W   75 KT  85 MPH - Category 1 (WSW Hilo, Hawaii)
 96H  04/1200Z 17.8N 146.5W   75 KT  85 MPH - Category 1 (WSW Hilo, Hawaii)
120H  05/1200Z 19.0N 151.5W   60 KT  70 MPH - Tropical Storm (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 1100 PM HST Tue Jul 30, 2019

High-resolution WindSat imagery from 0227 UTC gave quite a surprise when it arrived a few hours ago: Flossie is not as organized as it seemed. The low-level center was displaced about 40 n mi to the west of overshooting convective tops and mid-level rotation seen in infrared satellite images, the result of moderate to strong westerly shear. A 0513 UTC ASCAT-C pass also revealed an asymmetric wind field, with no tropical-storm-force winds in the southwestern quadrant. The initial intensity is held at 70 kt, mainly for the sake of continuity, but the ASCAT data and recent SATCON estimates suggest that it could be lower.

Flossie continues to move west-northwestward (285 degrees), now at a speed of 13 kt. A narrow mid-level ridge centered along 24N is forecast to build westward toward the Hawaiian Islands over the next 3 days, with the flow on the southern side, expected to keep Flossie moving west-northwestward or westward at a steady clip for the entire forecast period. The track guidance remains tightly clustered, and the new NHC forecast has only been nudged northward from the previous one to account for the more-apparent initial position.

It’s difficult at the moment to see how Flossie will be able to strengthen much in the coming days. The cyclone’s structure is already suffering from the effects of shear, and diagnostics from the SHIPS model suggest that the shear could increase further, or at least hold steady, during the next 48 hours. There’s an opportunity for the shear to decrease a bit in 2-3 days, but by that time, Flossie will have reached marginally warm waters with little to no ocean heat content. Given these less-than-ideal environmental factors, the NHC intensity forecast has again been reduced from the previous one, and it generally lies between the HCCA and the Florida State Superensemble. This solution is still near the high end of the guidance envelope and above the conventional intensity consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT  31/0900Z 13.5N 124.4W   70 KT  80 MPH- Category 1 (ESE Hilo, Hawaii)
 12H  31/1800Z 14.1N 126.3W   70 KT  80 MPH- Category 1 (ESE Hilo, Hawaii)
 24H  01/0600Z 14.8N 128.9W   75 KT  85 MPH- Category 1 (ESE Hilo, Hawaii)
 36H  01/1800Z 15.5N 131.6W   80 KT  90 MPH- Category 1 (ESE Hilo, Hawaii)
 48H  02/0600Z 16.1N 134.3W   80 KT  90 MPH- Category 1 (ESE Hilo, Hawaii)
 72H  03/0600Z 17.2N 139.9W   80 KT  90 MPH- Category 1 (ESE Hilo, Hawaii)
 96H  04/0600Z 18.0N 145.0W   75 KT  85 MPH- Category 1 (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 500 PM HST Tue Jul 30, 2019

Satellite images indicate that deep convection continues to pulse near the center of Flossie, with cloud-top temperatures to -92C observed during the past several hours. Microwave data show the center is just south of those overshooting tops, and about half a ragged eyewall is present. The initial wind speed is raised to 70 kt, which is a blend of the latest estimates from TAFB/SAB.

The cyclone continues to have difficulty closing off a complete eyewall, likely due to northwesterly shear and some dry air aloft as indicated by outflow boundaries noted in the northern semicircle. The environment is forecast to become less conducive late on Wednesday, possibly due to some of the outflow from Hurricane Erick impacting Flossie, and the predicted NHC intensity briefly levels off on Thursday. Thereafter, the upper-level winds do become lighter, but the center is still fairly close to a high-shear region, so only slight intensification is shown. Model guidance has generally come down quite a bit since the last cycle, which is consistent with the iffy environment, so the NHC forecast is reduced about 5 kt from the previous one in the first 48 hours. After 3 days, the NHC forecast indicates slow weakening after considering marginal water temperatures and light/moderate westerly shear, although it should be mentioned the models are in poor agreement on the long-range intensity.

A 0107 UTC SSMI/S pass nicely shows the center of Flossie, which helps to give a more confident initial motion of 285/12. A mid-level ridge to the north of the hurricane is expected to be the primary steering during the next several days, yielding a general west-northwest motion. A turn to the west is probable at long-range since the ridge builds westward ahead of the cyclone. The models remain in fairly good agreement, so the latest NHC track forecast is basically an update of the previous one, shaded a bit toward the ECMWF.

FORECAST POSITIONS AND MAX WINDS

INIT  31/0300Z 12.8N 122.6W   70 KT  80 MPH - Category 1 (WSW Hilo, Hawaii)
 12H  31/1200Z 13.3N 124.5W   75 KT  85 MPH - Category 1 (WSW Hilo, Hawaii)
 24H  01/0000Z 14.0N 127.0W   80 KT  90 MPH - Category 1 (WSW Hilo, Hawaii)
 36H  01/1200Z 14.7N 129.7W   85 KT 100 MPH - Category 2 (WSW Hilo, Hawaii)
 48H  02/0000Z 15.5N 132.5W   85 KT 100 MPH - Category 2 (WSW Hilo, Hawaii)
 72H  03/0000Z 16.7N 138.1W   90 KT 105 MPH - Category 3 (WSW Hilo, Hawaii)
 96H  04/0000Z 17.5N 143.5W   80 KT  90 MPH - Category 1 (WSW Hilo, Hawaii)
120H  05/0000Z 18.0N 148.5W   70 KT  80 MPH - Category 1 (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 1100 AM HST Tue Jul 30, 2019

Deep convection associated with Flossie has been increasing in both intensity and coverage during the past several hours, and the cyclone now consists of a well-organized central dense overcast with some broken outer bands. The Dvorak classifications from TAFB and SAB are now both 4.0/65 kt and, based on this data, Flossie has been upgraded to a 65-kt hurricane.

Flossie is moving westward at about 12 kt steered by a mid-level ridge that is situated to the north of the tropical cyclone. This ridge is expected to be the primary steering feature during the next several days, and it should cause Flossie to move westward to west-northwestward at about the same forward speed through the weekend. The models are tightly clustered, and only small changes were made to the previous NHC track forecast. This forecast lies near the consensus aids, which usually have the lowest track errors.

The cyclone is expected to be in generally favorable environmental conditions to strengthen during the next day or so. After that time, however, the sea surface temperatures beneath the hurricane gradually decrease and the wind shear is expected to increase a little. A combination of these factors should end the strengthening trend and induce a slow weakening by the weekend. The NHC intensity forecast is a tad lower than the previous one, but it lies near the high end of the model guidance, in best agreement with the HCCA and IVDR consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT  30/2100Z 12.3N 121.3W   65 KT  75 MPH - Category 1 (WSW Hilo, Hawaii)
 12H  31/0600Z 12.7N 123.2W   75 KT  85 MPH - Category 1 (WSW Hilo, Hawaii)
 24H  31/1800Z 13.4N 125.6W   85 KT 100 MPH - Category 2 (WSW Hilo, Hawaii)
 36H  01/0600Z 14.2N 128.3W   90 KT 105 MPH - Category 3 (WSW Hilo, Hawaii)
 48H  01/1800Z 15.0N 130.9W   90 KT 105 MPH - Category 3 (WSW Hilo, Hawaii)
 72H  02/1800Z 16.3N 136.7W   90 KT 105 MPH - Category 3 (WSW Hilo, Hawaii)
 96H  03/1800Z 17.3N 142.0W   85 KT 100 MPH - Category 2 (WSW Hilo, Hawaii)
120H  04/1800Z 18.1N 147.3W   75 KT  85 MPH - Category 1 (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 500 AM HST Tue Jul 30, 2019

Convection associated with Flossie increased overnight, and the cyclone’s cloud-top pattern has become more symmetric. However, AMSR data from about 6 hours ago indicated that most of the deep convection was limited to the southern semicircle of the cyclone, indicative of northerly shear, and an SSMIS pass at 1213 appeared to confirm that this is still the case. The latest Dvorak intensity estimates from TAFB and SAB are 55 kt and 65 kt, respectively, so the initial intensity of Flossie has been increased to 60 kt, as a compromise of those two assessments.

Overall, there is little change in the track or intensity forecast reasoning. Flossie is moving westward on the south side of a broad mid-level ridge that extends across most of the eastern Pacific. All of the guidance indicates that Flossie will move generally west-northwestward for the next 5 days, and the model spread is low. Very little changes were made to the NHC track forecast which is near the various multi-model consensus aids, and confidence in the track forecast is high.

Conversely, there is low confidence in the intensity forecast. Flossie appears to have about 36 to 48 hours in a marginally conducive environment to intensify, and the HWRF even explicitly forecasts that rapid intensification could occur. An increase in northerly shear in about 48 h could then inhibit further intensification, however the GFS and ECMWF suggest that the shear could decrease again by the end of the forecast period. The spread in the intensity guidance is very high, particularly beyond 48 h, with the dynamical models generally higher than the statistical guidance. No major changes were made to the intensity forecast, which is near HCCA and FSSE at all forecast hours, however larger changes could be required in future advisories given the high uncertainty in the forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  30/1500Z 12.2N 120.5W   60 KT  70 MPH - Tropical torm (WSW Hilo, Hawaii)
 12H  31/0000Z 12.5N 122.5W   70 KT  80 MPH - Category 1 (WSW Hilo, Hawaii)
 24H  31/1200Z 13.1N 125.0W   85 KT 100 MPH - Category 2 (WSW Hilo, Hawaii)
 36H  01/0000Z 13.8N 127.6W   90 KT 105 MPH - Category 2 (WSW Hilo, Hawaii)
 48H  01/1200Z 14.6N 130.3W   95 KT 110 MPH - Category 2 (WSW Hilo, Hawaii)
 72H  02/1200Z 16.1N 136.0W   90 KT 105 MPH - Category 2 (WSW Hilo, Hawaii)
 96H  03/1200Z 17.3N 141.7W   90 KT 105 MPH - Category 2 (WSW Hilo, Hawaii)
120H  04/1200Z 18.5N 147.0W   80 KT  90 MPH - Category 1 (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 1100 PM HST Mon Jul 29,  2019

Flossie’s overall appearance has not changed much over the past several hours. There continues to be some dry air evident over the northern semicircle that is entraining into the storm’s circulation and the SHIPS guidance also suggests there is about 10 kt of northerly shear across the system. This has resulted in most of the deep convection being confined to the southern semicircle for much of tonight. The initial intensity remains 55 kt, which is in agreement with the latest subjective satellite intensity estimates from both TAFB and SAB.

The motion over the past 12 hours has been just south of due west, or 265/15 kt. A turn to the west to the west-northwest is expected by later today or tonight and this general motion is expected to continue for the remainder of the forecast period as Flossie is steered by a broad mid-level ridge to its north. The track guidance remains tightly clustered, and the official NHC forecast track is very close to the previous one.

Recently, deep convection has been trying to wrap around the northeastern portion of the circulation. If this trend were to continue, then strengthening would likely resume in the near term. There is about a 48-hour window remaining for Flossie to significantly intensify in a fairly favorable environment. The lastest SHIPS model Rapid Intensification Index (RII) shows a greater than 50 percent chance for Flossie to intensify by 25 kt over a 24 hour period. However, Flossie will need to consolidate its inner core soon if this rapid strengthening is to occur. The official NHC forecast calls for steady strengthening through much of today, followed by a 24 hour period of more rapid strengthening that would make Flossie a category 3 hurricane in 48 hours. After 48 hours, increasing shear and marginal SSTs are expected to cause a weakening trend to begin. The official intensity forecast is close to the previous forecast as well as the NOAA corrected consensus, HCCA, and the Florida State Superensemble consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT  30/0900Z 12.2N 119.3W   55 KT  65 MPH - Tropical Storm (ESE Socorro Island, Mexico)
 12H  30/1800Z 12.3N 121.3W   65 KT  75 MPH - Category 1 (WSW Hilo, Hawaii)
 24H  31/0600Z 12.8N 123.9W   80 KT  90 MPH - Category 1 (WSW Hilo, Hawaii)
 36H  31/1800Z 13.6N 126.5W   90 KT 105 MPH - Category 2 (WSW Hilo, Hawaii)
 48H  01/0600Z 14.3N 129.1W  100 KT 115 MPH - Category 3 (WSW Hilo, Hawaii)
 72H  02/0600Z 16.1N 134.8W   95 KT 110 MPH - Category 2 (WSW Hilo, Hawaii)
 96H  03/0600Z 17.5N 140.5W   90 KT 105 MPH - Category 2 (WSW Hilo, Hawaii)
120H  04/0600Z 18.5N 145.5W   80 KT  90 MPH - Category 1 (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 1100 AM HST Mon Jul 29, 2019

The GOES-17 water vapor presentation, along with the upper-level satellite-derived winds, reveals that an upper anticyclone just to the north of Flossie is still producing modest vertical wind shear. This inhibiting wind pattern is also confirmed by a recent METOP-B AMSU pass that depicted a lack of deep convection in the northern portion of the cyclone. The subjective and objective intensity estimates, along with an earlier 1517 UTC SATCON analysis, yield an initial intensity of 45 kt for this advisory.

Flossie is forecast to gradually intensify into a category 2 hurricane in 3 days, then commence a slow weakening trend as the cyclone moves into a more stable and drier air mass, along with increasing wind shear. The official intensity forecast is based on a blend of the NOAA HCCA and the Florida State Superensemble, and is similar to the previous package.

The initial motion is estimated to be westward, or 270/16 kt. A strong, deep-layer ridge anchored to the north of Flossie should influence a generally westward to west-northwestward motion during the next 5 days. The track guidance remains in very good agreement and the official NHC track forecast is again hedged toward the NOAA HCCA and the TVCN multi-model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  29/2100Z 12.5N 116.2W   45 KT  50 MPH - Tropical Storm (ESE Socorro Island, Mexico)
 12H  30/0600Z 12.4N 118.3W   55 KT  65 MPH - Tropical Storm (ESE Socorro Island, Mexico)
 24H  30/1800Z 12.6N 120.8W   65 KT  75 MPH - Category 1 (WSW Hilo, Hawaii)
 36H  31/0600Z 13.2N 123.4W   75 KT  85 MPH - Category 1 (WSW Hilo, Hawaii)
 48H  31/1800Z 13.8N 125.9W   85 KT 100 MPH - Category 2 (WSW Hilo, Hawaii)
 72H  01/1800Z 15.5N 131.3W   95 KT 110 MPH - Category 2 (WSW Hilo, Hawaii)
 96H  02/1800Z 17.0N 136.9W   90 KT 105 MPH - Category 2 (WSW Hilo, Hawaii)
120H  03/1800Z 18.3N 142.0W   85 KT 100 MPH - Category 2 (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 500 AM HST Mon Jul 29, 2019

A series of fortuitous microwave images was helpful in locating the center of circulation and revealed significant banding improvements in the south semicircle portion of the cyclone. Although the subjective satellite T-number estimates only yield an intensity of 35 kt, subsequent SATCON analysis of 50 kt and the ADT estimate of 47 kt support increasing the initial intensity to 45 kt for this advisory.

The ocean is warm and the shear is low, therefore, strengthening should continue and Flossie is forecast to become a hurricane in 24 hours. The GFS and ECMWF Decay SHIPS and the global models are showing increasing northerly vertical shear beyond the 48-hour period, which should curtail the intensification rate through the remainder of the forecast period. Both the NOAA HCCA and IVCN multi-model intensity consensus reflect this trend, and the official forecast was adjusted downward just a bit from the last advisory to agree with these models. It’s still worth noting, however, that Flossie could undergo rapid intensification during the next 48 hours, as indicated by a 40 percent probability of that occurring in the SHIPS RI guidance.

Tropical Storm Force Winds Tropical Storm Erick Tropical Storm Flossie July 28 2019
Tropical Storm Force Winds Tropical Storm Erick Tropical Storm Flossie July 28, 2019

The initial motion is estimated to be westward, or 270/16 kt. A deep-layer ridge is well-established and anchored to the north of the cyclone, and should steer Flossie generally westward to west-northwestward through the entire forecast period. The model suite remains tightly clustered and no adjustments have been made to the previous forecast, which again is close to the better performing TVCN and HCCA consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT  29/1500Z 12.5N 114.6W   45 KT  50 MPH- Tropical Storm (ESE Socorro Island, Mexico)
 12H  30/0000Z 12.4N 116.9W   55 KT  65 MPH- Tropical Storm (ESE Socorro Island, Mexico)
 24H  30/1200Z 12.3N 119.5W   65 KT  75 MPH - Category 1 (WSW Hilo, Hawaii)
 36H  31/0000Z 12.7N 122.2W   70 KT  80 MPH - Category 1 (WSW Hilo, Hawaii)
 48H  31/1200Z 13.3N 124.7W   75 KT  85 MPH - Category 1 (WSW Hilo, Hawaii)
 72H  01/1200Z 14.7N 129.8W   85 KT 100 MPH - Category 2 (WSW Hilo, Hawaii)
 96H  02/1200Z 16.1N 135.4W   90 KT 105 MPH - Category 2 (WSW Hilo, Hawaii)
120H  03/1200Z 17.5N 141.0W   90 KT 105 MPH - Category 2 (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 1100 PM HST Sun Jul 28, 2019

Over the past several hours, deep convection has developed near the center of circulation with a large curved band composed of cloud tops as cold as -80 C enveloping the western semicircle of the cyclone. A recent ASCAT-C scatterometer pass partially captured the northeastern quadrant of the system and measured winds of 30 kt over 75 n mi from the center and it is likely that higher winds were occurring at that time in the unsampled area closer to the center. In addition, the mean of the subjective Dvorak satellite intensity estimates have increased to tropical storm force and therefore the depression has been upgraded to Tropical Storm Flossie with an initial intensity of 35 kt.

The initial motion is 275/17 kt. Ridging will persist north of the cyclone throughout the next several days which will continue to steer it west to west-northwestward with some decrease in forward speed by later today as the ridge weakens slightly. The track guidance is in very good agreement and the official NHC forecast track is similar to the previous forecast which is very near the center of the consensus aids.

The environment around Flossie is favorable for strengthening over the next 72 hours or so, and if the current deep convection can persist near the center today during the diurnal minimum, then the inner core of the cyclone will likely become well established over the next 24 hours. This would allow for steady strengthening to occur, with Flossie becoming a hurricane sometime on Tuesday. Although not implicitly shown in the forecast, it is possible that Flossie could undergo rapid intensification during the next 72 hours which could result in intensities higher than currently forecast at those time frames. By day 4, the cyclone is forecast to move over marginal sea surface temperatures and into a drier, more stable environment while undergoing increasing northwesterly shear. This should result in a weakening trend beginning around hour 96 of the forecast period. The official NHC intensity forecast was changed little from the previous forecast, and remains on the higher end of the intensity guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  29/0900Z 12.5N 113.0W   35 KT  40 MPH - Tropical Storm (ESE Socorro Island, Mexico)
 12H  29/1800Z 12.7N 115.6W   45 KT  50 MPH - Tropical Storm (ESE Socorro Island, Mexico)
 24H  30/0600Z 12.6N 118.5W   55 KT  65 MPH - Tropical Storm (ESE Socorro Island, Mexico)
 36H  30/1800Z 12.8N 121.1W   65 KT  75 MPH - Category 1 (WSW Hilo, Hawaii)
 48H  31/0600Z 13.3N 123.7W   75 KT  85 MPH - Category 1 (WSW Hilo, Hawaii)
 72H  01/0600Z 14.5N 128.9W   95 KT 110 MPH - Category 2 (WSW Hilo, Hawaii)
 96H  02/0600Z 15.8N 134.5W   95 KT 110 MPH - Category 2 (WSW Hilo, Hawaii)
120H  03/0600Z 17.5N 140.5W   90 KT 105 MPH - Category 2 (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 900 PM MDT Sun Jul 28, 2019

Conventional and microwave satellite imagery indicates that the depression has again changed little in organization since the last advisory. The circulation remains broad, with apparent multiple vorticity centers rotating around the mean center, and the convection is in a loosely curved band over the northern semicircle. Various subjective and objective satellite intensity estimates are in the 30-35 kt range, and based on the unchanged organization the initial intensity is held at 30 kt.

The initial motion is 285/18. Deep-layer ridging to the north of the cyclone should steer it generally westward to west-northwestward through the forecast period, with some decrease in the forward speed after 24 h when it moves south of a slight weakness in the ridge. The track guidance is very tightly clustered and has changed little from the last advisory. Thus, the new NHC track forecast track is similar to the previous track and lies near the various consensus models.

The cyclone is expected to be in a nearly ideal environment for strengthening for at least the next 3 days, and the intensity guidance suggests a good chance of rapid intensification once an inner core becomes established. Given the current structure, it is expected that it will take 12-24 h for the inner core to form. Based on this and the guidance, the new NHC intensity forecast calls for steady strengthening for the first 24 h, followed by a faster intensification from 24-72 h. The new forecast is again increased above the previous forecast, and it lies near the upper edge of the guidance. It should be noted that once rapid intensification starts, the system could strengthen faster than currently forecast and reach category 3 or higher intensity. After 72 h, the forecast track takes the system over slightly cooler water and into an area of northwesterly shear, and the intensity forecasts calls for slow weakening during this time.

FORECAST POSITIONS AND MAX WINDS

INIT  29/0300Z 12.2N 111.0W   30 KT  35 MPH - Tropical Depression (ESE Socorro Island, Mexico)
 12H  29/1200Z 12.6N 113.7W   35 KT  40 MPH - Tropical Storm (ESE Socorro Island, Mexico)
 24H  30/0000Z 12.6N 116.8W   45 KT  50 MPH - Tropical Storm (ESE Socorro Island, Mexico)
 36H  30/1200Z 12.6N 119.4W   60 KT  70 MPH - Tropical Storm (WSW Hilo, Hawaii)
 48H  31/0000Z 12.8N 121.9W   75 KT  85 MPH - Category 1 (WSW Hilo, Hawaii)
 72H  01/0000Z 13.8N 127.1W   95 KT 110 MPH - Category 2 (WSW Hilo, Hawaii)
 96H  02/0000Z 15.0N 132.5W   95 KT 110 MPH - Category 2 (WSW Hilo, Hawaii)
120H  03/0000Z 16.5N 138.5W   90 KT 105 MPH - Category 2 (WSW Hilo, Hawaii)

NWS National Hurricane Center Miami FL 300 PM MDT Sun Jul 28, 2019

The depression has not changed much in organization since the previous advisory. The system has a broad circulation, with the low-level center located near the southeastern edge of a long convective band. Dvorak classifications are now a consensus T2.0 from TAFB and SAB, which supports maintaining an initial intensity of 30 kt. This is also in good agreement with just-received ASCAT-C data.

Various objective analyses suggest that the shear over the system is light, but that doesn’t appear to be the case based on high-level cloud motions seen on visible satellite imagery. Even with the depression’s fast forward speed, the center is chasing the convection out ahead of it. Given the cyclone’s current structure, only slow strengthening is anticipated during the next 24 hours while the depression continues to become better organized. Once an inner core forms, faster strengthening is likely due to low shear and warm waters, and the cyclone is forecast to become a hurricane just after 48 hours. In fact, SHIPS Rapid Intensification indices indicate that there is about a 40 percent chance that the cyclone’s winds will increase by at least 65 kt during the next 3 days. Therefore, the NHC intensity forecast has been raised from the previous one, especially after 48 hours, and most closely follows the HWRF and the European version of the SHIPS model, which lie above the intensity consensus and near the upper bound of the guidance envelope.

The initial motion is still fast–285/17 kt–due to the strength of the mid-level high to the north. Ridging is expected to keep the cyclone on a westward or west-northwestward heading for the entire 5-day forecast period, with some decrease in forward speed as it moves south of a weakness in the ridge. The track models are still tightly clustered, and the NHC track forecast is very close to HCCA and the other multi-model consensus aids, which also ends up being very close to the previous official forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  28/2100Z 11.5N 109.1W   30 KT  35 MPH - Tropical Depression (ESE Socorro Island, Mexico)
 12H  29/0600Z 11.9N 111.9W   35 KT  40 MPH - Tropical Depression (ESE Socorro Island, Mexico)
 24H  29/1800Z 12.1N 115.0W   40 KT  45 MPH - Tropical Storm (ESE Hilo. Hawaii)
 36H  30/0600Z 12.1N 117.9W   50 KT  60 MPH - Tropical Storm (ESE Hilo. Hawaii)
 48H  30/1800Z 12.1N 120.5W   60 KT  70 MPH - Tropical Storm (ESE Hilo. Hawaii)
 72H  31/1800Z 12.8N 125.6W   85 KT 100 MPH - Category 1 (ESE Hilo. Hawaii)
 96H  01/1800Z 14.0N 131.0W   90 KT 105 MPH - Category 1 (ESE Hilo. Hawaii)
120H  02/1800Z 15.5N 136.5W   90 KT 105 MPH - Category 1 (ESE Hilo. Hawaii)

NWS National Hurricane Center Miami FL 900 AM MDT Sun Jul 28, 2019

First-light visible satellite images have revealed that the area of low pressure located southwest of the coast of Mexico has developed a well-defined center of circulation. The convective pattern has also increased in the organization, with a pronounced band wrapping from the west to north of the center. Dvorak intensity estimates are T2.0/30 kt from SAB and T1.5/25 kt from TAFB, and advisories are being initiated on a 30-kt tropical depression.

Tropical Depression Seven-E is moving quickly along the southern periphery of mid-level ridging that is centered along the U.S/Mexico border, and its initial motion estimate is 285/18 kt. A weakness in the ridge west of the Baja California peninsula should allow the cyclone to slow down some after 24 hours, but the trajectory is expected to be either westward or west-northwestward for the entire 5-day forecast period. There is very little spread among the track models, and this initial NHC forecast has generally been placed between the various multi-model consensus models and the HFIP Corrected Consensus aid (HCCA).

The convective pattern and upper-level cloud motions suggest that there’s a little bit of shear over the system from the east-northeast, but that shear should abate over the next 24 hours. The cyclone will also be over deep warm water, with sea surface temperatures remaining above 27 degrees Celsius for the entire forecast period. As a result, steady strengthening is anticipated, and the NHC intensity forecast is slightly above the IVCN intensity consensus and close to the HCCA guidance for much of the forecast period. The depression is forecast to become a tropical storm later today, and it is likely to become a hurricane in 2 to 3 days.

FORECAST POSITIONS AND MAX WINDS

INIT  28/1500Z 11.2N 107.5W   30 KT  35 MPH - Tropical Depression (ESE Socorro Island, Mexico)
 12H  29/0000Z 11.8N 110.4W   35 KT  40 MPH - Tropical Storm (ESE Hilo. Hawaii)
 24H  29/1200Z 12.1N 113.8W   40 KT  45 MPH - Tropical Storm (ESE Hilo. Hawaii)
 36H  30/0000Z 12.1N 116.7W   45 KT  50 MPH - Tropical Storm (ESE Hilo. Hawaii)
 48H  30/1200Z 12.0N 119.3W   55 KT  65 MPH - Tropical Storm (ESE Hilo. Hawaii)
 72H  31/1200Z 12.5N 124.5W   70 KT  80 MPH - Category 1 (ESE Hilo. Hawaii)
 96H  01/1200Z 13.5N 130.0W   80 KT  90 MPH - Category 1 (ESE Hilo. Hawaii)
120H  02/1200Z 15.0N 135.5W   90 KT 105 MPH - Category 2 (ESE Hilo. Hawaii)

If this system is named it will be Tropical Storm Flossie.

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Video: 11 a.m. update on Tropical Depression Flossie

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