Tropical Storm Miriam

Tropical Depression Miriam Track 0500 Hours September 2 2018
Tropical Depression Miriam Track 0500 Hours September 2 2018
Tropical Depression Miriam Satellite 0500 Hours September 2 2018
Tropical Depression Miriam Satellite 0500 Hours September 2 2018

NWS Central Pacific Hurricane Center Honolulu HI 500 AM HST Sun Sep 02 2018

The center of Miriam(see Saturday video below) has been completely devoid of deep convection for almost 24 hours as nearly 50 kt of southwesterly vertical wind shear has taken its toll on the system. The latest subjective Dvorak current intensity estimates range from unclassifiable by SAB to T1.5/25 kt by JTWC, and T2.0/30 kt by PHFO. The most recent UW-CIMSS ADT yielded an estimated intensity of 25 kt. Based on a blend of these estimates, the initial intensity is lowered to 30 kt for this advisory.

The initial motion is 320 deg / 12 kt. A broad mid- to upper-level trough to the northwest of Miriam will maintain the very strong vertical wind shear during the next couple of days. Since Miriam has transitioned to a shallow low-level cloud swirl, it is now being steered more toward the northwest under the influence of a deep subtropical ridge located to the northeast. This northwestward motion will likely persist through Monday. The latest forecast track is close to the previous advisory, and remains near the middle of the guidance envelope and close to the consensus model guidance, TVCE and HCCA. Under the hostile vertical wind shear and decreasing SSTs, Miriam will continue weakening. The latest intensity forecast weakens Miriam at a slightly slower rate than almost all of the guidance, and is closest to the GFS output. Note that Miriam is forecast to become a remnant low later today, followed by dissipation late Monday.Tropical Depression Miriam Distances 0500 Hours September 2 2018

FORECAST POSITIONS AND MAX WINDS
 
INIT  02/1500Z 26.1N 143.9W   30 KT  35 MPH
 12H  03/0000Z 27.3N 145.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 24H  03/1200Z 28.6N 147.4W   25 KT  30 MPH...POST-TROP/REMNT LOW
 36H  04/0000Z 29.7N 149.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  04/1200Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 1100 AM HST Sat Sep 01 2018

Under the effects of strong vertical wind shear, the low level center of Miriam  is now completely exposed, and a diminishing amount of deep convection is confined to the north quadrant. Subjective Dvorak current intensity estimates came in at 3.0/45 kt from HFO and JTWC, while SAB gave a 3.5/55 kt. All final T numbers were lower. CIMSS ADT yielded a 3.0, and its earlier SATCON from 1642Z produced 48 kt. Given the significant decay in the satellite presentation, the initial intensity will be lowered to 50 kt, making Miriam a rapidly weakening tropical storm.

The initial motion is north-northwest (345 degrees) at 11 kt, and a turn toward the northwest is under way. A mid to upper level trough to the northwest of Miriam is producing strong, southwesterly vertical wind shear of 40 to 50 kt according to analyses, and the shear will likely continue to increase through the next 18 hours. As Miriam becomes increasingly shallow and less intense under the effects of the shear, the system will be steered toward the northwest under a greater influence of a deep ridge located far to the northeast. The general northwestward motion will persist through the duration of the tropical cyclone’s existence, which will be a few days at best. The forecast track lies just right of the middle of the guidance envelope between HCCA and TVCE. Under the hostile vertical wind shear and decreasing SSTs, Miriam is expected to weaken to a post-tropical remnant low on Sunday, with dissipation likely on Monday. The official forecast weakens Miriam at a slightly slower rate than most guidance through the next 36 hours and is close to HMNI and AVNI.

FORECAST POSITIONS AND MAX WINDSTropical Storm Miriam Distances 1100 Hours September 1 2018
 
INIT  01/2100Z 23.3N 141.5W   50 KT  60 MPH - Tropical Storm (ENE Honolulu, Hawaii)
 12H  02/0600Z 24.7N 142.5W   40 KT  45 MPH - Tropical Storm (ENE Honolulu, Hawaii)
 24H  02/1800Z 26.3N 144.1W   30 KT  35 MPH - Tropical Storm (ENE Honolulu, Hawaii)
 36H  03/0600Z 27.6N 146.1W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  03/1800Z 28.7N 148.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  04/1800Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 500 AM HST Sat Sep 01 2018

Shear continues to profoundly affect the core of Miriam   this morning, with the low level circulation center (LLCC) now mostly exposed along the southwest flank of diminishing deep convection. UW-CIMSS reports 41 kt of vertical wind shear across this system, up from 34 kt last evening. Good outflow exists only to the north through north-northeast, consistent with the shear direction. Subjective Dvorak current intensity estimates decreased to 4.0/65 kt from PHFO and SAB, and to 3.5/55 kt from JTWC. ADT from UW-CIMSS was 65 kt. Initial intensity for this advisory is set at 65 kt which, like last time, represents weakening but may still be a bit too high given the rapidly deteriorating satellite presentation.

Initial motion is 355/10 kt as Miriam continues northward between an upper trough to the northwest and a deep ridge to the northeast. Track guidance continues to depict a turn toward the north-northwest through Sunday and toward the northwest on Monday. The guidance envelope is rather tight through 48 hours, with HWRF depicting a sharper turn toward the left as it forecasts rapid dissipation of this system and a greater role for low level steering in the near term. In contrast, ECMWF lies along the right side of the guidance envelope. The forecast track closely follows the previous one, neatly following TCVE consensus, but adjusted slightly to the right through 24 hours to account for initial motion.Hurricane Miriam Distances 0500 Hours September 1 2018

Miriam will continue to weaken in the face of increasing shear and sub-26 degree C SSTs through the forecast period, with this system forecast to dissipate at 72 hours. We expect Miriam will weaken to a tropical storm later today before becoming a post tropical remnant low early Monday. Some guidance dissipate Miriam earlier, with DSHIP and LGME calling for this at 36 and 48 hours, respectively. Our intensity curve follows HMNI through 12 hours, then along HWRF through dissipation.

FORECAST POSITIONS AND MAX WINDS
 
INIT  01/1500Z 22.2N 141.3W   65 KT  75 MPH - Category 1 (ENE Honolulu, Hawaii)
 12H  02/0000Z 23.6N 141.9W   55 KT  65 MPH - Tropical Storm (ENE Honolulu, Hawaii)
 24H  02/1200Z 25.4N 143.4W   40 KT  45 MPH - Tropical Storm (ENE Honolulu, Hawaii)
 36H  03/0000Z 27.1N 145.2W   30 KT  35 MPH - Tropical Storm (ENE Honolulu, Hawaii)
 48H  03/1200Z 28.7N 147.2W   25 KT  30 MPH...POST-TROP/REMNT LOW

NWS Central Pacific Hurricane Center Honolulu HI 1100 PM HST Fri Aug 31 2018

DISCUSSION AND OUTLOOK

At 1100 PM HST (0900 UTC), the center of Hurricane Miriam was located near latitude 20.9 North, longitude 141.2 West. Miriam is moving toward the north near 9 mph (15 km/h) and this motion is expected to continue tonight, followed by a turn toward the northwest and a slight increase in forward speed on Saturday and Sunday.

Maximum sustained winds are near 85 mph (140 km/h) with higher gusts. Rapid weakening will occur tonight through Sunday, and Miriam is forecast to become a post-tropical remnant low Monday.

Hurricane-force winds extend outward up to 25 miles (35 km) from the center and tropical-storm-force winds extend outward up to 110 miles (175 km).

The estimated minimum central pressure is 981 mb (28.97 inches).

NWS Central Pacific Hurricane Center Honolulu HI 1100 AM HST Fri Aug 31 2018

Miriam  has been resilient under increasing vertical wind shear. A ragged, cloud-filled eye has reappeared, despite southwesterly vertical wind shear of about 25 to 35 kt according to SHIPS and CIMSS, respectively. Subjective Dvorak current intensity estimates came in at 5.0/90 kt across the board from HFO, SAB, and JTWC, while CIMSS ADT yielded 80 kt. Given the longer term improvement in the satellite presentation but noting the periodic filling of the eye during the past several hours, the initial intensity has been raised to 85 kt, which may be conservative.

The initial motion estimate is slightly east of due north (010 degrees) at 9 kt. An SSMIS pass from 1352Z suggested some tilt toward the northeast with height, which led to the placement of the center near the southwestern edge of the eye as seen on geostationary satellite imagery. Through the next 24 hours, Miriam will continue to be steered northward by a mid to upper level trough to the northwest and a deep ridge to the northeast. Later Saturday, Miriam will begin a turn toward the northwest. This will occur as the steering flow of the weakening system becomes increasingly influenced by the low level ridge that will shift to the north of Miriam. A general northwestward motion is expected to persist until dissipation. The track was nudged to the right of the prior forecast and lies near the middle of the guidance envelope, close to HCCA and TVCE.Hurricane Miriam Distances 1100 Hours August 31 2018

The slight increase in intensity will be short-lived. The already vigorous, southwesterly vertical wind shear will increase through the next 36 to 48 hours. In addition, SSTs, which are currently running around 26.5 C, will steadily decrease along the forecast track. Expect weakening to commence later today, with a sharp decrease in intensity tonight through Sunday. The intensity forecast goes nearly down the middle of the guidance envelope and is close to the statistical models and FSSE. On this forecast, Miriam will be a tropical storm by Saturday and will weaken to a remnant low late Sunday or Monday.

FORECAST POSITIONS AND MAX WINDS
 
INIT  31/2100Z 19.2N 141.1W   85 KT 100 MPH - Category 2 (ESE Hilo, Hawaii)
 12H  01/0600Z 20.6N 141.2W   75 KT  85 MPH - Category 1 (ESE Hilo, Hawaii)
 24H  01/1800Z 22.6N 141.7W   55 KT  65 MPH - Tropical Storm (ESE Hilo, Hawaii)
 36H  02/0600Z 24.6N 143.0W   40 KT  45 MPH - Tropical Storm (ESE Hilo, Hawaii)
 48H  02/1800Z 26.6N 144.7W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
 72H  03/1800Z 30.0N 148.6W   30 KT  35 MPH...POST-TROP/REMNT LOW

NWS Central Pacific Hurricane Center Honolulu HI 1100 PM HST Thu Aug 30 2018

The satellite presentation of Miriam  has changed little over the past 6 hours, but a slight improvement in the convective cloud coverage over the low level circulation center appears to have occurred during the past several hours. A large area of -65 to -80C cloud tops remain over the difficult to locate low level circulation center. Several microwave passes since 30/2330Z have been helpful in confidently determining the center location of Miriam as well as estimating the motion of the system this evening, with a 0346Z Windsat and 0636Z MHS Metop-A pass particularly useful. Subjective Dvorak fixes from PHFO, SAB, and JTWC all came in with intensity estimates of 4.5 (77 knots) with the Advanced Dvorak Technique from UW-CIMSS slightly lower at 4.3 (72 knots). Several images around 31/06Z showed the center sufficiently within the deeper colder cloud tops to yield a T5.0 (90 knots). Based on the slight improvement in the convective cloud coverage over Miriam, and several images around the synoptic hour yielding higher intensity estimates, the initial intensity for this advisory has been weighted slightly higher than the intensity estimates indicated from the various agencies. The initial intensity has been raised to 80 knots with this advisory with a motion of 360/07 knots.Hurricane Norman Distances 2300 Hours August 30 2018

Miriam is being steered by a large subtropical ridge to the northeast and a mid-upper level trough to the north and northwest. A general northward motion is expected to continue tonight through Friday night as the system remains deep and intact following the deep layer steering flow. Strong southwesterly shear is then expected to decouple the system by late Friday night or early Saturday, and this is expected to result in a turn toward the northwest with Miriam being steered by the low level trade wind flow. The official forecast has been shifted slightly to the right through 48 hours to better align with the HWRF, TVCE, HCCA and GFS which indicate a fairly deep circulation. Beyond 48 hours the official forecast track lies roughly on top of the previous forecast as the system becomes increasingly shallow and steered by the low level trade wind flow.

It appears that the window for Miriam to intensify has closed, with the latest UW-CIMSS vertical shear analysis showing 21 knots of southwesterly shear over the core of the system. The hurricane is expected to slowly weaken tonight and Friday as shear steadily increases. Rapid weakening is then forecast Friday night and Saturday as Miriam moves into a region of strong southwesterly shear of 35 to 50 knots and moves over unfavorable sea surface temperatures below 26C. Miriam is forecast to become a remnant low by late Sunday.

FORECAST POSITIONS AND MAX WINDS
 
INIT  31/0900Z 17.4N 141.5W   80 KT  90 MPH - Category 1 (ESE Hilo, Hawaii)
 12H  31/1800Z 18.7N 141.3W   75 KT  85 MPH - Category 1 (ESE Hilo, Hawaii)
 24H  01/0600Z 20.5N 141.5W   65 KT  75 MPH - Category 1 (ESE Hilo, Hawaii)
 36H  01/1800Z 22.3N 142.3W   50 KT  60 MPH - Tropical Storm (ESE Hilo, Hawaii)
 48H  02/0600Z 24.2N 143.6W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
 72H  03/0600Z 27.7N 147.3W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  04/0600Z 31.0N 152.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  05/0600Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 1100 AM HST Thu Aug 30 2018

Miriam’s satellite appearance improved early this morning, when a banding type eye appeared in traditional satellite imagery shortly after a well-developed eye was evident in a 1326Z GPM microwave overpass. Cold cloud tops briefly encircled a portion of the eye, but the eye is now cloud-filled once again. Subjective Dvorak intensity estimates from HFO/SAB/GTW trended up to 4.5/77 kt, and the initial intensity estimate for this advisory has been increased to 75 kt. The initial motion estimate is 330/7 kt.

The window for additional strengthening is expected to soon close as Miriam moves north into an area of very strong vertical wind shear and decreasing SSTs. Miriam will move nearly due north in the deep southerly flow between a ridge to the east and a trough to the north. This gradient will also increase vertical wind shear to near 30 kt in 24-36 h. SSTs currently near 28C will drop below 26C after 48 h, with the cumulative effects leading to a fairly fast rate of weakening after tomorrow. The shallow remnant of Miriam is then expected to make a turn toward the northwest, primarily steered by the low-level trade wind flow, and is expected to be close to dissipation by the end of the forecast period. The official track forecast is on the left hand side of the guidance envelope, but has been nudged to the right at almost all time frames, to be more in line with the TVCE and HCCA ensembles. The intensity forecast follows trends presented by all reliable guidance.Hurricane Miriam Distances 1100 Hours August 30 2018

FORECAST POSITIONS AND MAX WINDS
 
INIT  30/2100Z 15.7N 141.6W   75 KT  85 MPH - Category 1 (ESE Hilo, Hawaii)
 12H  31/0600Z 17.0N 141.7W   80 KT  90 MPH - Category 1 (ESE Hilo, Hawaii)
 24H  31/1800Z 18.7N 141.5W   75 KT  85 MPH - Category 1 (ESE Hilo, Hawaii)
 36H  01/0600Z 20.4N 141.6W   60 KT  70 MPH - Tropical Storm (ESE Hilo, Hawaii)
 48H  01/1800Z 22.1N 142.5W   45 KT  50 MPH - Tropical Storm (ESE Hilo, Hawaii)
 72H  02/1800Z 25.0N 145.0W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
 96H  03/1800Z 28.0N 149.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  04/1800Z 30.0N 154.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

NWS Central Pacific Hurricane Center Honolulu HI 1100 PM HST Wed Aug 29 2018

The satellite presentation of Miriam has improved slightly since the previous advisory, with deep convection remaining over the difficult to locate low level circulation center. The latest subjective Dvorak intensity estimates from PHFO, SAB and JTWC ranged from 4.0 (65 knots) to 4.5 (77 knots) while the Advanced Dvorak Technique from UW-CIMSS came in at 3.5 (55 knots). Since the satellite presentation has improved slightly since the previous advisory, the initial intensity will be increased to 70 knots with this advisory, which correlates well with a blend of the intensity estimates. The initial motion is set at 300/07 knots. Miriam is being steered by a large subtropical ridge to the northeast of the system and a deep mid-upper level trough to the north-northwest.

Miriam is expected to track off to the northwest tonight then make a turn toward the north Thursday through Friday night. The increasing west-southwesterly shear should result in a decoupling of the system by early Saturday, and this is expected to result in a turn toward the northwest and eventually west Saturday through Monday as Miriam becomes influenced primarily by the low level trade wind flow. The official forecast for this advisory is nearly identical to the previous advisory and closely follows the consensus guidance.Hurricane Miriam Distances 2300 Hours August 29 2018

The environment will be conducive for additional intensification of Miriam over the next 24 hours, with shear values remaining low, sea surface temperatures holding around 28C, while the system moves over a region of higher Ocean Heat Content. As a result the official forecast calls for slight intensification over the next 24 hours, followed by slow and steady weakening between 24 and 36 hours as Miriam begins to feel the effects of strengthening west- southwesterly shear. Beyond 36 hours the intensity forecast will show fairly rapid weakening as shear values increase into the 30 to 45 knot range, while the system moves over marginal sea surface temperatures of 26C or below.

FORECAST POSITIONS AND MAX WINDS
 
INIT  30/0900Z 14.7N 141.1W   70 KT  80 MPH - Category 1 (ESE Hilo, Hawaii)
 12H  30/1800Z 15.4N 141.6W   75 KT  85 MPH - Category 1 (ESE Hilo, Hawaii)
 24H  31/0600Z 16.8N 141.6W   80 KT  90 MPH - Category 1 (ESE Hilo, Hawaii)
 36H  31/1800Z 18.4N 141.5W   70 KT  80 MPH - Category 1 (ESE Hilo, Hawaii)
 48H  01/0600Z 19.9N 141.9W   55 KT  65 MPH - Tropical Storm (ESE Hilo, Hawaii)
 72H  02/0600Z 23.0N 144.0W   40 KT  45 MPH - Tropical Storm (ESE Hilo, Hawaii)
 96H  03/0600Z 25.5N 147.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  04/0600Z 27.0N 152.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

 

NWS National Hurricane Center Miami FL 200 PM PDT Wed Aug 29 2018

The satellite presentation of Miriam  has significantly improved over the past 12 hours or so. Several microwave images received since the release of the previous advisory revealed a significant increase in organization with convection wrapping nearly completely around the center. Recent visible satellite images have shown hints of an eye, but the surrounding convective tops have warmed somewhat. Subjective and objective Dvorak intensity estimates all support hurricane strength, and the initial intensity is increased to 65 kt for this advisory.

Satellite fixes show that Miriam has slowed down and is moving westward or 270/8 kt. The hurricane is near the western edge of the subtropical ridge and is forecast to turn west-northwestward very soon. A large mid- to upper-level trough located northeast of the Hawaiian Islands should cause Miriam to turn northwestward, then northward over the next couple of days, and the dynamical models are in good agreement through 72 hours. After that time, model differences remain as the ECMWF continues to take a deeper cyclone much faster northward than the remainder of the guidance. The NHC forecast continues to lean toward the solution of a weaker cyclone turning northwestward or west-northwestward near the end of the forecast period. The updated NHC forecast is once again south of the model consensus at days 4 and 5 and is in best agreement with the GFS ensemble mean.

INIT  29/2100Z 14.0N 139.7W   65 KT  75 MPH - Category 1 (ESE Hilo, Hawaii)
 12H  30/0600Z 14.4N 140.7W   70 KT  80 MPH - Category 1 (ESE Hilo, Hawaii)
 24H  30/1800Z 15.3N 141.3W   75 KT  85 MPH - Category 1 (ESE Hilo, Hawaii)
 36H  31/0600Z 16.7N 141.5W   70 KT  80 MPH - Category 1 (ESE Hilo, Hawaii)
 48H  31/1800Z 18.4N 141.5W   60 KT  70 MPH - Category 1 (ESE Hilo, Hawaii)
 72H  01/1800Z 21.5N 142.7W   40 KT  45 MPH - Tropical Storm (ESE Hilo, Hawaii)
 96H  02/1800Z 24.7N 145.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  03/1800Z 27.0N 149.5W   25 KT  30 MPH...POST-TROP/REMNT LOW

Miriam has about another 12-24 h over warm water and within a light to moderate wind shear environment in which to strengthen. After that time, a significant increase in southwesterly shear is anticipated and Miriam is forecast to weaken fairly quickly between 36 and 72 hours. Miriam should reach SSTs below 26C by 96 h and should degenerate into a remnant low by that time. Miriam will move into the Central Pacific Basin shortly and this is last NHC advisory on this system.

NWS National Hurricane Center Miami FL 800 AM PDT Wed Aug 29 2018

Although Miriam remains a sheared tropical cyclone, recent geostationary satellite data and a 1002 UTC AMSR2 microwave overpass indicates that there has been some improvement in the structure of the cyclone. The microwave data showed an increase in banding over the eastern portion of the circulation and less separation between the convection and the low-level center. Therefore, the initial intensity is increased to 60 kt, which is a blend of the most recent subjective Dvorak classifications and objective T-numbers from UW/CIMSS. The northwesterly shear over the cyclone appears to have abated slightly, and a further slight reduction in shear could allow Miriam to reach hurricane strength within the next 24-36 h. Most of the intensity guidance agrees, and the NHC intensity forecast has been increased slightly for the first 36 h. After that time, increasing shear and cooler waters are expected to cause Miriam to weaken fairly quickly and the system is forecast to become a remnant low by day 4.

Miriam continues to move westward or 275/10 kt. The cyclone is approaching the western edge of the subtropical ridge, and the global models indicate that Miriam will slow down and turn west-northwestward very soon. By Thursday, a large mid- to upper-level trough to the northeast of the Hawaiian Islands is expected to cause Miriam to turn northwestward, then northward through 72 hours. At days 3 and beyond, there continues to be significant model differences with the ECMWF still taking Miriam faster and much farther northward, while the GFS moves a much weaker Miriam westward. Since Miriam is forecast to weaken and become a shallow system around that time, the NHC forecast leans toward the more westward scenario, but is not as far south and west as the GFS. The new NHC track is south of the various consensus aids at day 5, and is in best agreement with the GFS ensemble mean and UKMET model.

FORECAST POSITIONS AND MAX WINDS

INIT  29/1500Z 14.2N 139.4W   60 KT  70 MPH - Tropical Storm (ESE Hilo, Hawaii)
 12H  30/0000Z 14.4N 140.6W   65 KT  75 MPH - Category 1 (ESE Hilo, Hawaii)
 24H  30/1200Z 15.1N 141.6W   65 KT  75 MPH - Category 1 (ESE Hilo, Hawaii)
 36H  31/0000Z 16.3N 142.0W   65 KT  75 MPH - Category 1 (ESE Hilo, Hawaii)
 48H  31/1200Z 17.9N 142.1W   60 KT  70 MPH - Tropical Storm (ESE Hilo, Hawaii)
 72H  01/1200Z 21.0N 142.9W   45 KT  50 MPH - Tropical Storm (ESE Hilo, Hawaii)
 96H  02/1200Z 23.8N 145.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  03/1200Z 26.7N 149.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

NWS National Hurricane Center Miami FL 200 AM PDT Wed Aug 29 2018

At face value, Miriam  seems to be getting a little better organized. Its convective canopy has been expanding during the past few hours, and continuous lightning strokes have been detected within a well-defined mid-level circulation. However, a 0637 UTC METOP-B microwave pass shows that Miriam remains a sheared cyclone, with the low-level center running out ahead of the deep convection. Still, with the expanding convection, Dvorak estimates from TAFB and SAB have risen to T3.5, and the initial intensity is set at 55 kt.

Miriam is moving westward, or 275/11 kt, near the western end of the subtropical ridge. A deep-layer low located northeast of the Hawaiian Islands is expected to cause Miriam to slow down and turn sharply northwestward and northward during the next 48 hours. The models are in excellent agreement on this scenario. After day 3, however, there are significant differences among the guidance, with the GFS taking a shallow cyclone almost due westward and the ECMWF continuing to accelerate a deeper Miriam northward on the east side of the deep-layer low. With these models being the most acute outliers, the NHC forecast track thinking continues to lie close to the tight clustering of the Florida State Superensemble, HCCA, and TVCX consensus aids.

There is also greater-than-normal uncertainty in the intensity forecast. The SHIPS and LGEM models show northwesterly shear persisting over Miriam and only strengthen the cyclone slightly during the next 24-36 hours. The HWRF and HCCA models are still showing more significant strengthening, making Miriam a hurricane over the next day or two. I was tempted to explicitly show Miriam becoming a hurricane in the official forecast, but I decided to hold off since the cyclone just hasn’t been able to display an improved structure as of yet. Even if some strengthening does occur, vertical shear is expected to increase substantially from 48 hours onward, which will cause fast weakening and Miriam likely degenerating into a remnant low by day 5.

The National Hurricane Center in Miami, Florida, is issuing advisories on Tropical Storm Miriam, located about 1150 miles east-southeast of Hilo, Hawaii. Miriam is forecast to move into the Central Pacific Hurricane Center area of responsibility later today.

FORECAST POSITIONS AND MAX WINDS

INIT  29/0900Z 14.2N 138.4W   55 KT  65 MPH - Tropical Storm (ESE Hilo, Hawaii)
 12H  29/1800Z 14.4N 139.8W   60 KT  70 MPH - Tropical Storm (ESE Hilo, Hawaii)
 24H  30/0600Z 14.9N 141.1W   60 KT  70 MPH - Tropical Storm (ESE Hilo, Hawaii)
 36H  30/1800Z 15.8N 141.9W   60 KT  70 MPH - Tropical Storm (ESE Hilo, Hawaii)
 48H  31/0600Z 17.2N 142.0W   60 KT  70 MPH - Tropical Storm (ESE Hilo, Hawaii)
 72H  01/0600Z 20.4N 142.5W   50 KT  60 MPH - Tropical Storm (ESE Hilo, Hawaii)
 96H  02/0600Z 23.0N 144.5W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
120H  03/0600Z 26.5N 148.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

NWS National Hurricane Center Miami FL 200 AM PDT Tue Aug 28 2018

Miriam’s  cloud pattern has still not improved very much, with microwave data showing the low-level center still slightly displaced from the deep convection due to about 10 kt of northwesterly shear. Dvorak estimates from TAFB and SAB, as well as the UW-CIMSS SATCON, all remain near 55 kt, which will remain Miriam’s initial intensity. Miriam is expected to remain over warm waters and in a relatively low-shear environment for the next 48-72 hours, which should allow the cyclone to strengthen modestly over the next few days. At 72 hours and beyond, Miriam will encounter significantly stronger shear ahead of an amplifying mid- to upper-level trough northeast of the Hawaiian Islands, and the cyclone will also move over sub-26C waters. These conditions should cause a rather quick weakening trend on days 4 and 5, with Miriam barely hanging on as a tropical storm by the end of the forecast period. The intensity guidance has decreased somewhat on this forecast cycle, probably because Miriam has less time before it reaches stronger shear. The updated NHC intensity forecast lies between the HCCA guidance and the IVCN intensity consensus, with the forecast peak intensity just slightly below that of the previous advisory.

The initial motion is due westward, or 270/10 kt, with Miriam located along the southern periphery of the subtropical ridge. The amplifying trough northeast of Hawaii is breaking down the ridge and should cause Miriam to turn sharply toward the northwest and north between days 2 and 4. There are significant speed differences among the models by days 4 and 5, related to how deep Miriam is when it interacts with the deep-layer trough. The ECMWF, which maintains a deeper, stronger vortex, shoots Miriam quickly northward, ending up more than 600-700 nm north of where the GFS and HWRF models have the cyclone by day 5. Given where the consensus aids lie between those two extremes, the updated NHC track  forecast has been slowed down a bit from the previous forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  28/0900Z 14.0N 133.5W   55 KT  65 MPH - Tropical Storm (ESE Hilo, Hawaii)
 12H  28/1800Z 14.0N 135.1W   60 KT  70 MPH - Tropical Storm (ESE Hilo, Hawaii)
 24H  29/0600Z 14.1N 137.1W   70 KT  80 MPH - Category 1 (ESE Hilo, Hawaii)
 36H  29/1800Z 14.4N 138.8W   75 KT  85 MPH - Category 1 (ESE Hilo, Hawaii)
 48H  30/0600Z 15.1N 140.1W   80 KT  90 MPH - Category 1 (ESE Hilo, Hawaii)
 72H  31/0600Z 17.9N 141.0W   80 KT  90 MPH - Category 1 (ESE Hilo, Hawaii)
 96H  01/0600Z 21.5N 141.5W   55 KT  65 MPH - Tropical Storm (ESE Hilo, Hawaii)
120H  02/0600Z 26.0N 144.0W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 200 PM PDT Mon Aug 27 2018

Miriam has become a little better organized since the last advisory, and the convective banding has become better defined around the low-level center. However, this has not yet resulted in an increase of the various satellite intensity estimates, which remain mostly near 55 kt. Based on this, the initial intensity remains a possibly conservative 55 kt. Satellite imagery continues to indicate northwesterly to northerly vertical shear affecting Miriam, with cirrus clouds from the outer band to the north blowing into the central convection.

The initial motion is 270/13. A large low- to mid-level ridge to the north of Miriam should continue to steer it westward for the next 36-48 h with some decrease in forward speed. After that, a large mid- to upper-level low to the northeast of the Hawaiian Islands is expected to cause the ridge to break between 140W-150W, with Miriam turning northwestward and north-northwestward in response. The track guidance is in good agreement on this scenario, but there remain some differences in Miriam’s forward speed after recurvature between the faster ECMWF/UKMET and the slower GFS. The new forecast track is similar to the previous track through 72 h, then is nudged a little to the east based on an eastward shift in the consensus models.

The global models continue to suggest a gradual increase in northwesterly shear over Miriam during the next day or so, followed by decreased shear from 24-48 h. There is some divergence in the intensity guidance through 72 h, with the SHIPS/LGEM models showing less strengthening than the HWRF/HMON/corrected consensus models. This part of the new intensity forecast is little changed from the previous forecast and lies between these two model camps. After 72 h, increasing southwesterly shear and cooler waters are expected to cause Miriam to weaken.

FORECAST POSITIONS AND MAX WINDS

INIT  27/2100Z 14.0N 131.8W   55 KT  65 MPH - Tropical Storm (ESE Hilo, Hawaii)
 12H  28/0600Z 14.0N 133.5W   65 KT  75 MPH - Category 1 (ESE Hilo, Hawaii)
 24H  28/1800Z 13.9N 135.5W   70 KT  80 MPH - Category 1 (ESE Hilo, Hawaii)
 36H  29/0600Z 14.0N 137.5W   75 KT  85 MPH - Category 1 (ESE Hilo, Hawaii)
 48H  29/1800Z 14.5N 139.0W   85 KT 100 MPH - Category 2 (ESE Hilo, Hawaii)
 72H  30/1800Z 16.5N 141.0W   85 KT 100 MPH - Category 2 (ESE Hilo, Hawaii)
 96H  31/1800Z 20.0N 142.0W   75 KT  85 MPH - Category 1 (ESE Hilo, Hawaii)
120H  01/1800Z 24.5N 143.5W   50 KT  60 MPH - Tropical Storm (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 800 AM PDT Mon Aug 27 2018

The convective structure of Miriam  has become better organized this morning, with a continued increase in overall banding. An earlier AMSR2 microwave overpass also revealed a well-defined band over the southeastern and southern portions of the circulation but there was some evidence of northwesterly shear with the center near the northwestern edge of the primary convective band. The initial intensity has been increased to 55 kt, which is supported by a Dvorak Data T-number of 3.5 from TAFB, earlier AMSU data, and recent UW/CIMSS ADT estimates of T3.7 (59 kt).

Satellite fixes indicate that Miriam is moving westward or 270 degrees at 12 kt. The cyclone should remain on a westward heading over the next 48 hours while it is steered by a large deep-layer ridge to the north. After that time, a large mid- to upper-level low to the northeast of the Hawaiian Islands is expected to produce a break in the ridge between 140W-150W. This should cause Miriam to turn northwestward, then north-northwestward between days 3 through 5. The track guidance is in good agreement on this scenario, but there are some differences in Miriam’s forward speed after recurvature begins. The ECMWF and UKMET take Miriam much faster northward than the remainder of the dynamical models, and the NHC track forecast is once again close to the various consensus aids at 72 h and beyond to account for the speed differences.

The global models suggest that there will be a gradual increase in northwesterly shear over Miriam during the next day or so, however, this is not expected to prevent the cyclone from becoming a hurricane within the next 24 hours. The moderate shear is forecast to relax by Tuesday night, which should allow for additional intensification. The intensity guidance is not quite as aggressive as before, and the NHC intensity forecast, which lies between the IVCN intensity consensus model and the HFIP corrected consensus, has been adjusted slightly downward. Increasingly southwesterly vertical wind shear and cooler waters are expected to cause Miriam to weaken late in the forecast period.

FORECAST POSITIONS AND MAX WINDS

INIT  27/1500Z 13.9N 130.5W   55 KT  65 MPH - Tropical Storm (ESE Hilo, Hawaii)
 12H  28/0000Z 13.9N 132.3W   65 KT  75 MPH - Category 1 (ESE Hilo, Hawaii)
 24H  28/1200Z 13.8N 134.3W   70 KT  80 MPH - Category 1 (ESE Hilo, Hawaii)
 36H  29/0000Z 13.9N 136.3W   75 KT  85 MPH - Category 1 (ESE Hilo, Hawaii)
 48H  29/1200Z 14.1N 138.1W   85 KT 100 MPH - Category 2 (ESE Hilo, Hawaii)
 72H  30/1200Z 15.5N 140.8W   85 KT 100 MPH - Category 2 (ESE Hilo, Hawaii)
 96H  31/1200Z 18.7N 141.8W   75 KT  85 MPH - Category 1 (ESE Hilo, Hawaii)
120H  01/1200Z 23.3N 143.2W   55 KT  65 MPH - Tropical Storm (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 200 PM PDT Sun Aug 26 2018

Tropical Storm Miriam  continues to gradually become better organized. The latest visible satellite images show a well-defined curved band that wraps about three-quarters of the way around the center. Despite the improvement in organization, very recent ASCAT passes show maximum winds of about 35 kt. Therefore, the initial wind speed is held at 40 kt as a compromise between the ASCAT data and the higher Dvorak-based estimates.

The tropical storm is moving westward at about 12 kt. This westward motion should continue during the next few days while a deep-layer ridge remains anchored to the north of the tropical cyclone. After that time, the storm is forecast to turn to the northwest and then the north as a mid- to upper-level low causes a significant break in the subtropical ridge. Although the models agree on this scenario, there are some differences in where and when Miriam will make the northward turn. The NHC track forecast lies near the middle of the guidance envelope, near the consensus aids.

Steady strengthening is likely during the next couple of days due to the favorable environmental factors of low wind shear, high levels of moisture, and warm SSTs of 27-28 deg C. The latest intensity models all show Miriam becoming a hurricane, and the HWRF model shows the cyclone reaching major hurricane strength. The NHC intensity forecast continues to lean toward the higher end of the model guidance, and it is in best agreement with HFIP Corrected Consensus Approach model. By the end of the forecast period, when Miriam begins gaining latitude, slow weakening is expected due to a decrease in SSTs and higher shear.

FORECAST POSITIONS AND MAX WINDS

INIT  26/2100Z 13.6N 126.6W   40 KT  45 MPH - Tropical Storm (WSW Acapulco, Mexico)
 12H  27/0600Z 13.6N 128.4W   50 KT  60 MPH - Tropical Storm (WSW Acapulco, Mexico)
 24H  27/1800Z 13.7N 130.6W   65 KT  75 MPH - Category 1 (ESE Hilo, Hawaii)
 36H  28/0600Z 13.7N 132.7W   80 KT  90 MPH - Category 1 (ESE Hilo, Hawaii)
 48H  28/1800Z 13.7N 134.8W   90 KT 105 MPH - Category 2 (ESE Hilo, Hawaii)
 72H  29/1800Z 13.7N 138.7W   90 KT 105 MPH - Category 2 (ESE Hilo, Hawaii)
 96H  30/1800Z 15.8N 141.1W   85 KT 100 MPH - Category 1 (ESE Hilo, Hawaii)
120H  31/1800Z 19.7N 141.7W   80 KT  90 MPH - Category 1 (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 800 AM PDT Sun Aug 26 2018

Deep convection associated with the tropical cyclone has continued to become better organizedthis morning, with a significant increase in banding noted in conventional satellite imagery. An earlier AMSR2 microwave overpass also revealed the increase in banding, but the low-level center was located near the northeastern portion of the main convective mass. A Dvorak satellite intensity estimate of T2.5 (35 k) was the basis for the 1200 UTC synoptic intensity, but with the continued increase in organization, the initial wind speed for this advisory has been set to 40 kt.

Miriam is moving westward or 275/11 kt. The tropical storm should remain on a general westward heading during the next few days while it remains to the south of a deep-layer ridge. The orientation of the ridge may shift more west-southwestward within the next day or so, which could steer the tropical storm on a track slightly south of due west. The bulk of the dynamical model guidance has shifted southward, so the NHC forecast track has been adjusted accordingly through the first 3 days. After that time, a weakness in the subtropical ridge between 140W-145W longitude is expected to cause Miriam to turn northwestward, then north-northwestward by the end of the forecast period. The latter portion of the official forecast is similar to the previous advisory and is in best agreement with the HFIP corrected consensus model.

The environment ahead of Miriam is expected to remain favorable for strengthening. The tropical storm will be traversing SSTs of 27-28C and within low vertical wind shear conditions. The NHC intensity forecast calls for steady intensification during the next few days and is at the upper-end of the intensity guidance. Although the various rapid intensification prediction techniques are not particularly bullish, perhaps due to the low initial intensity of the cyclone, it would not be surprising if the tropical storm went through a period of rapid intensification within the next couple of days. The NHC intensity forecast is closest to the more aggressive HWRF and HMON dynamical models.

FORECAST POSITIONS AND MAX WINDS

INIT  26/1500Z 13.2N 125.3W   40 KT  45 MPH - Tropical Storm (WSW Acapulco, Mexico)
 12H  27/0000Z 13.3N 127.1W   50 KT  60 MPH - Tropical Storm (WSW Acapulco, Mexico)
 24H  27/1200Z 13.5N 129.4W   60 KT  70 MPH - Tropical Storm (WSW Acapulco, Mexico)
 36H  28/0000Z 13.5N 131.5W   70 KT  80 MPH - Category 1 (WSW Acapulco, Mexico)
 48H  28/1200Z 13.5N 133.6W   80 KT  90 MPH - Category 1 (ESE Hilo, Hawaii)
 72H  29/1200Z 13.5N 137.6W   85 KT 100 MPH - Category 1 (ESE Hilo, Hawaii)
 96H  30/1200Z 14.9N 140.5W   90 KT 105 MPH - Category 2 (ESE Hilo, Hawaii)
120H  31/1200Z 18.5N 142.0W   85 KT 100 MPH - Category 1 (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 500 AM PDT Sun Aug 26 2018

For the eastern North Pacific…east of 140 degrees west longitude:

The National Hurricane Center is issuing advisories on newly formed Tropical Depression Fifteen-E, located more than 1000 miles west-southwest of the southern tip of the Baja California peninsula.

This storm will become Tropical Storm Miriam.

NWS National Hurricane Center Miami FL 200 AM PDT Sun Aug 26 2018

Various satellite data over the past several hours, including recent ASCAT scatterometer surface-wind data, indicate that the well-defined low pressure area located about 1000 nmi southwest of the southern tip of the Baja California peninsula has become much better organized, and has developed into a tropical depression. A small CDO-like feature has formed over the well-defined center depicted in the ASCAT data, and a recent burst of cold cloud tops of -80C have also developed just west of the center. The initial intensity of 30 kt is based on 0458Z and 0558Z ASCAT wind data, which indicated winds of 28-30 kt were located 35-40 nmi west and southwest of the low-level center.

The initial motion estimate is 280/10 kt. The depression is expected to remain south of a strong deep-layer subtropical ridge for the next 96 hours, resulting in a general westward motion at a slightly faster forward speed. By day 5, the cyclone is forecast to move into a break in the ridge created by a broad mid-/upper-level trough that is forecast to dig southward out of the northern Pacific between 140W-145W longitude. The forecast track lies essentially down the middle of the guidance envelope, which is just north of the consensus model TVCE and the GFS model, but south of the ECMWF and UKMET models. The HRWF and HMON models were not being available for the TVCE consensus on this cycle, so some significant adjustments to the track in the next advisory may be required.

The cyclone has a radius of maximum winds (RMW) of 35-40 nmi based on the recent ASCAT data. The combination of the modest RMW, low vertical wind shear of less than 10 kt, a very moist mid-level environment, and sea-surface temperatures above 28 deg C, favors steady intensification and even the possibility of rapid strengthening. Since this is the first forecast, however, the intensity forecast is on the conservative side and calls for a climatological increase of one T-number or 20 kt every 24 h for the next 48 hours, which is above all of the intensity guidance except for the Navy COAMPS (CTCI) model. By 96-120 hours, the intensity is leveled off due to possible entrainment of drier air and an increase in southwesterly vertical wind shear.

FORECAST POSITIONS AND MAX WINDS

INIT  26/0900Z 13.3N 124.1W   30 KT  35 MPH - Tropical Storm (WSW Acapulco, Mexico)
 12H  26/1800Z 13.5N 126.0W   40 KT  45 MPH - Tropical Storm (WSW Acapulco, Mexico)
 24H  27/0600Z 13.7N 128.4W   50 KT  60 MPH - Tropical Storm (WSW Acapulco, Mexico)
 36H  27/1800Z 13.9N 130.6W   60 KT  70 MPH - Tropical Storm (WSW Acapulco, Mexico)
 48H  28/0600Z 14.1N 132.6W   70 KT  80 MPH - Category 1 (ESE Hilo, Hawaii)
 72H  29/0600Z 14.3N 136.6W   80 KT  90 MPH - Category 1 (ESE Hilo, Hawaii)
 96H  30/0600Z 14.9N 140.1W   90 KT 105 MPH - Category 2 (ESE Hilo, Hawaii)
120H  31/0600Z 17.4N 141.9W   90 KT 105 MPH - Category 2 (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 500 PM PDT Sat Aug 25 2018

For the eastern North Pacific…east of 140 degrees west longitude:

1. An area of low pressure located just over 1000 miles southwest of the southern tip of the Baja California peninsula appears to be becoming a little better organized. Although satellite data indicate that a well-defined surface circulation has not yet formed, environmental conditions appear conducive for additional development, and a tropical depression is likely to form within the next few days while the system moves westward around 10 mph. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…high...70 percent.

2. A broad low pressure system located about 500 miles south of Acapulco, Mexico, continues to produce a large area of disorganized showers and thunderstorms. Slow development of this system is expected over the next several days, and a tropical depression could form by the middle of next week while it moves westward or west-northwestward at 10 mph. * Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…medium…60 percent.

NWS National Hurricane Center Miami FL 500 AM PDT Sat Aug 25 2018

For the eastern North Pacific…east of 140 degrees west longitude:

1. Shower activity has changed little since yesterday in association with a broad area of low pressure located about 1000 miles southwest of the southern tip of the Baja California peninsula. Gradual development of this system is possible during the next several days, and a tropical depression could form by the middle of next week while the system moves westward around 10 mph. * Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…medium...50 percent.

2. Another broad area of low pressure is located several hundred miles south of Acapulco, Mexico. Some slow development of this system is possible over the next several days while it moves westward or west-northwestward at 10 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…20 percent.

NWS National Hurricane Center Miami FL 500 PM PDT Fri Aug 24 2018

For the eastern North Pacific…east of 140 degrees west longitude:

1. An elongated area of low pressure located about 1000 miles south-southwest of the southern tip of the Baja California peninsula continues to produce disorganized showers and a few thunderstorms. Gradual development of this system is possible during the next several days, and a tropical depression could form by the middle of next week while the system moves westward around 10 mph.
* Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…medium…50 percent.

2. An area of low pressure could form well to the east-southeast of the Hawaiian Islands in a couple of days. Development of this system, if any, should be slow to occur next week while it moves westward or west-northwestward at about 10 mph.
* Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…10 percent.

NWS National Hurricane Center Miami FL 1100 AM PDT Fri Aug 24 2018

For the eastern North Pacific…east of 140 degrees west longitude:

1. A broad area of low pressure located about 1000 miles west-southwest of the southern tip of the Baja California peninsula continues to produce disorganized shower activity. Gradual development of this system is possible during the next several days while the disturbance moves westward around 10 mph. * Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…medium…50 percent.

2. An area of low pressure could form within the next few days well to the east-southeast of the Hawaiian Islands. Development, if any, of this system should be slow to occur next week while it moves westward or west-northwestward at about 10 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…20 percent.

NWS National Hurricane Center Miami FL 500 AM PDT Fri Aug 24 2018

For the eastern North Pacific…east of 140 degrees west longitude:

1. A trough of low pressure located about 1000 miles west-southwest of the southern tip of the Baja California peninsula is producing disorganized showers and thunderstorms. Gradual development of this system is possible during the next several days while the disturbance moves westward around 10 mph. * Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…medium…40 percent.

2. An area of low pressure could form in a few days well to the east-southeast of the Hawaiian Islands. Some slow development of this system is possible next week while it moves westward or west-northwestward at about 10 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…30 percent.

NWS National Hurricane Center Miami FL 500 PM PDT Thu Aug 23 2018

For the eastern North Pacific…east of 140 degrees west longitude:

1. A trough of low pressure is producing disorganized showers and thunderstorms several hundred miles south-southwest of the southern tip of the Baja California Peninsula. Some gradual development of this system is possible through early next week while the disturbance moves westward around 10 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low...30 percent.

2. An area of low pressure could form in a few days well to the east-southeast of the Hawaiian Islands. Some slow development of this system is possible early next week while it moves westward or west-northwestward at about 10 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…20 percent.

NWS National Hurricane Center Miami FL 1100 AM PDT Thu Aug 23 2018

For the eastern North Pacific…east of 140 degrees west longitude: 

1. An area of low pressure could form this weekend several hundred miles southwest of the southern tip of Baja California Sur. Gradual development of this system is possible thereafter while the disturbance moves westward at about 10 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…20 percent.

2. A second area of low pressure could form in a few days well to the east-southeast of the Hawaiian Islands. Some slow development of this system is possible early next week while it moves westward or west-northwestward at about 10 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…20 percent.

NWS National Hurricane Center Miami FL 500 AM PDT Thu Aug 23 2018

For the eastern North Pacific…east of 140 degrees west longitude:

1. An area of low pressure could form this weekend several hundred miles southwest of the southern tip of Baja California Sur. Gradual development of this system is possible thereafter while the disturbance moves westward at about 10 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…20 percent.

2. A second area of low pressure could form in a few days well to the east-southeast of the Hawaiian Islands. Some slow development of this system is possible early next week while it moves westward or west-northwestward at about 10 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low...20 percent.

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