Tropical Storm Wanda

Post Tropical Storm Wanda Track 1500 Hours November 07 2021
Post Tropical Storm Wanda Track 1500 Hours November 07 2021

Tropical Storm Wanda Wind Speed FieldTropical Storm WandaNWS National Hurricane Center Miami FL 300 PM GMT Sun Nov 07, 2021 (see video below)

Wanda is no longer generating deep convection in association with its low-level circulation. In fact, most of the colder cloud tops seen on satellite over the center right now are actually upper-level cirrus associated with a cold frontal boundary part of a larger mid-latitude cyclone southeast of Greenland. In addition, an 1156 UTC ASCAT-B pass over Wanda’s circulation shows that the north side is beginning to open up into a trough as the cold front is encroaching on the system. These above factors suggest that Wanda is no longer a tropical cyclone, and the system is now classified as a post-tropical low as of this advisory. The winds remain 35-kt based on the peak wind retrieval of 33-kt from the scatterometer data on the southeast side of the circulation.

The system has been accelerating to the northeast with the latest estimated motion at 045/22 kt. The post-tropical cyclone should continue to accelerate to the northeast until it merges with the baroclinic zone approaching it. A 12 hour point is provided for continuity and to indicate the transition to an extratropical cyclone, though its quite possible the system will be fully absorbed by the frontal boundary by then. The track guidance at 12 hours is tightly clustered, and the NHC track forecast at that time fame follows the consensus aids closely.

This is the last NHC advisory on Wanda.

FORECAST POSITIONS AND MAX WINDS

INIT  07/1500Z 40.2N  33.5W   35 KT  40 MPH - Post Tropical (WNW Vila do Corvo,Azores)
 12H  08/0000Z 43.5N  29.1W   35 KT  40 MPH - Post Tropical (WNW Vila do Corvo,Azores)
 24H  08/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 300 PM GMT Sat Nov 06, 2021 

The structure of Wanda has changed little since the last advisory, with a band of convection near the center in the northern semicircle and more isolated convective cells elsewhere near the center. The various objective and subjective satellite intensity estimates range from 30-47 kt. Given the spread and the unchanged structure, the initial intensity is held at 45 kt.

The initial motion is 180/5 kt. Satellite imagery shows a large mid-latitude low pressure system approaching Wanda from the west and northwest, which should cause the tropical cyclone to turn northeastward during the next 12 h. After that, Wanda is expected to accelerate toward the northeast. The current guidance is in good agreement on the direction of motion, although it is a little slower than the previous guidance. The new forecast track is similar to, but slightly slower than, the previous forecast.

Increasing upper-level divergence associated with the mid-latitude low should allow Wanda to strengthen slightly during the next 24 h. Afterwards, the cyclone is expected to merge with a cold front and become an extratropical low. The global models subsequently forecast this low to weaken to a trough by 60 h, and the new intensity forecast shows dissipation at that time. Otherwise, there are only minor adjustments to the previous intensity forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  06/1500Z 37.0N  38.2W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 12H  07/0000Z 37.6N  36.8W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 24H  07/1200Z 40.5N  33.0W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 36H  08/0000Z 45.3N  26.7W   50 KT  60 MPH - Post Tropical (WSW Brest,France)
 48H  08/1200Z 50.6N  18.1W   45 KT  50 MPH - Post Tropical (WSW Galway,Ireland)
 60H  09/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 900 AM GMT Fri Nov 05, 2021 

Wanda’s cloud pattern remains about the same as it was yesterday evening, with bands of moderately deep convection mainly over the western half of the circulation. Dry and stable air is apparently limiting convection over the eastern semicircle of the cyclone. The current intensity estimate is held at 45 kt for this advisory, which is somewhat higher than Dvorak estimates but in good agreement with earlier scatterometer observations. This seems reasonable given that the cloud pattern has changed little overnight.

The latest center fixes indicate that the cyclone is now moving east-southeastward, or 120/5 kt. Wanda is expected to turn southeastward today, and then southward on Saturday as a mid-tropospheric ridge builds to the north and west of the cyclone. After that time, a deep-layer trough is expected to approach Wanda, resulting in a turn to the northeast at an increasing forward speed. The official forecast is similar to the dynamical track model consensus.

Since Wanda should move over slightly warmer waters and the shear is not expected to increase during the next couple of days, this should allow the storm to at least maintain its intensity or strengthen a bit. After about 48 hours, vertical shear is predicted to increase significantly. However, baroclinic effects associated with an approaching strong front could offset the weakening process. By 72 hours, the global models indicate that Wanda will become embedded within the frontal zone, and thus have made the transition to an extratropical cyclone. The NHC intensity forecast is close to the latest corrected consensus model.

FORECAST POSITIONS AND MAX WINDS

INIT  05/0900Z 41.8N  38.0W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 12H  05/1800Z 40.3N  37.8W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 24H  06/0600Z 38.2N  37.9W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 36H  06/1800Z 37.8N  37.6W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 48H  07/0600Z 39.3N  35.3W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 60H  07/1800Z 43.0N  31.4W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 72H  08/0600Z 47.5N  26.5W   50 KT  60 MPH - Post Tropical (WSW Brest,France)
 96H  09/0600Z 53.0N  20.0W   45 KT  50 MPH - Post Tropical (WSW Galway,Ireland)
120H  10/0600Z...DISSIPATED

NWS National Hurricane Center Miami FL 900 PM GMT Thu Nov 04 2021

Wanda continues to maintain bands of moderately deep convection near the center, mainly over the northwestern semicircle. The cyclone also continues to show anticyclonic outflow. However, cold air clouds continue to wrap around the southern side of the circulation, and in the big picture Wanda still gives the appearance of being embedded in a larger-scale baroclinic low. There has been little change in the satellite intensity estimates since the previous advisory, so the initial intensity is held at 40 kt.

Wanda is starting its anticipated turn and the initial motion is now 045/5. During the next day or two, a narrow mid-latitude ridge is forecast to build to the northwest of the cyclone, and this should cause Wanda to turn southeastward and southward by the 48 h point. By 60-72 h, another mid-latitude trough approaching Wanda should cause a northeastward turn with acceleration, with this motion persisting through the end of the forecast period. The new guidance again shows a little more southward motion by 48 h than the previous guidance, and the new forecast track is adjusted a little southward near that time.

Little change in strength is likely during the next 24 h as Wanda remains over sea surface temperatures of near 20C. By 48 h, the southward motion brings the center over slightly warmer water, and at that time the cyclone should interact with an upper-level low that develops nearby. This combination could allow some strengthening, and the intensity forecast show modest strengthening from 24-48 h. Many of the guidance models continue to show more strengthening and a higher intensity than the official forecast between 48-72 h, and some adjustment may be needed to that part of the forecast in later advisories if this trend persists. Between 72-96 h, Wanda is expected to merge with a frontal system and become extratropical over the northeastern Atlantic.

FORECAST POSITIONS AND MAX WINDS
 
INIT  04/2100Z 42.4N  39.2W   40 KT  45 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 12H  05/0600Z 41.9N  38.7W   40 KT  45 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 24H  05/1800Z 40.1N  38.2W   40 KT  45 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 36H  06/0600Z 38.5N  38.1W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 48H  06/1800Z 38.0N  37.7W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 60H  07/0600Z 39.2N  35.9W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 72H  07/1800Z 42.6N  32.2W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 96H  08/1800Z 49.0N  23.0W   45 KT  50 MPH - Post Tropical (WSW Brest,France)
120H  09/1800Z 53.0N  12.5W   35 KT  40 MPH - Post Tropical (WSW Dingle,Ireland)

NWS National Hurricane Center Miami FL 300 PM GMT Thu Nov 04, 2021

Wanda continues to maintain bands of moderately deep convection near the center, and the cyclone continues to display anticyclonic outflow. However, cold air clouds are wrapping around the southern side of the circulation, and in the big picture Wanda appears to be embedded in a larger-scale baroclinic low. A recent ASCAT-A overpass suggests that the maximum winds are now near 40 kt, which is between the satellite intensity estimates from TAFB and SAB.

The initial motion is northward or 000/5 kt. During the next couple of days, a narrow mid-latitude ridge is forecast to build to the northwest of the cyclone, which should cause Wanda to turn southeastward and southward by the 48 h point. By 60-72 h, another mid-latitude trough approaching Wanda should finally cause the system to begin to accelerate northeastward, with this motion persisting through the end of the forecast period. The new guidance shows a little more southward motion by 48 h than the previous guidance, and the new forecast track is adjusted a little southward near that time.

Little change in strength is likely during the next 24 h as Wanda remains over sea surface temperatures of near 20C. By 48 h, the southward motion brings the center over slightly warmer water, and some modest strengthening is possible by that time. Many of the guidance models show more strengthening and a higher intensity than the official forecast between 48-72 h, and some adjustment may be needed to that part of the forecast in later advisories if this trend persists. By 96 h, Wanda is expected to merge with a frontal system and become extratropical over the northeastern Atlantic.

FORECAST POSITIONS AND MAX WINDS

INIT  04/1500Z 41.9N  39.6W   40 KT  45 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 12H  05/0000Z 42.1N  38.9W   40 KT  45 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 24H  05/1200Z 41.0N  38.0W   40 KT  45 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 36H  06/0000Z 39.1N  37.7W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 48H  06/1200Z 38.1N  37.7W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 60H  07/0000Z 38.7N  36.6W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 72H  07/1200Z 41.0N  33.7W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 96H  08/1200Z 48.5N  23.0W   45 KT  50 MPH - Post Tropical (WSW Brest,France)
120H  09/1200Z 51.5N  13.5W   40 KT  45 MPH - Post Tropical (WSW Dingle,Ireland)

NWS National Hurricane Center Miami FL 900 AM GMT Thu Nov 04, 2021 

Wanda continues to exhibit bands of moderately deep convection, and these bands are strongest most numerous over the western portion of the circulation. The upper-level outflow has become better defined, also over the western semicircle. Overall, however, the intensity of the convection has diminished slightly over the past several hours. The advisory intensity is held at 45 kt, which is in agreement with Dvorak Current Intensity numbers from both SAB and TAFB. This is also in good agreement with earlier scatterometer measurements.

The initial motion continues to be just east of north, or 010/8 kt along the eastern side of a mid-latitude shortwave trough. This trough is expected to weaken very soon and Wanda should slow its forward speed later this morning. During the next 48 hours, a narrow ridge is forecast to build to the northwest of the cyclone and force it to turn eastward tonight and then southward on Friday. By 72 hours, another mid-latitude trough approaching Wanda should finally cause the system to begin to accelerate northeastward. The dynamical model guidance is in reasonably good agreement on the evolution of the steering pattern over the next several days. There has been little change to the official track forecast, which remains close to the model consensus, and near the middle of the guidance envelope.

Although Wanda is located over cool 20-21 deg C sea surface temperatures, it has been able to maintain some deep convection and winds of 45 kt. On its projected path during the next day or two, water temperatures beneath Wanda are not likely to get much cooler and the upper-tropospheric temperatures are forecast to decrease somewhat. This could allow for some slight strengthening, as indicated by the official intensity forecast. In 4 to 5 days, the global models show the system becoming embedded in a frontal zone over the north Atlantic, so the NHC forecast calls for Wanda to revert back to extratropical status by that time.

FORECAST POSITIONS AND MAX WINDS

INIT  04/0900Z 41.5N  39.5W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 12H  04/1800Z 42.1N  39.3W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 24H  05/0600Z 41.7N  38.2W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 36H  05/1800Z 40.1N  37.5W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 48H  06/0600Z 38.4N  37.5W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 60H  06/1800Z 38.2N  37.0W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 72H  07/0600Z 39.8N  35.0W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 96H  08/0600Z 47.0N  26.0W   45 KT  50 MPH - Post Tropical (WSW Brest,France)
120H  09/0600Z 52.0N  16.0W   40 KT  45 MPH - Post Tropical (WSW Dingle,Ireland)

NWS National Hurricane Center Miami FL 900 PM GMT Wed Nov 03, 2021

Wanda’s overall convective pattern has continued to improve since the previous advisory with a curved convective band now wrapping almost completely around the center, resulting in a 50-60-nmi wide banded eye feature. However, the horizontal thickness of the convective band has been waxing and waning, and cloud tops are only around -50C to -55C. Satellite intensity estimates from TAFB and SAB are a consensus T3.0/45 kt, while UW-CIMSS SATCON intensity estimates range from 34 kt to 44 kt, respectively. Based on these data, Wanda’s intensity is being maintained at 45 kt. Although a distinct eye feature is now evident, which would suggest a stronger storm, a lower intensity is warranted since the cooler water beneath the cyclone is likely creating a more stable boundary layer, which is likely inhibiting the normal downward mixing of higher winds aloft. This physical assumption is supported by weaker wind speeds noted in earlier scatterometer surface wind data.

The initial motion estimate is a little east of due north, or 010/09 kt. There is no significant change to the previous forecast track and rationale. An approaching mid-/upper-level trough from the west should continue to lift Wanda northward for the next day or so, followed by slowing and a sharp turn to the east by Thursday night as the aforementioned trough weakens and lifts out to the north of the cyclone. Subsequent ridging behind the trough will then force Wanda southeastward to southward on Friday, followed by another abrupt turn and acceleration to the northeast on Saturday as a second and stronger deep-layer trough captures the cyclone. Despite this complexity in the evolving steering pattern, the latest NHC model guidance is in very agreement throughout the 120-h forecast period on this track scenario. The new NHC forecast track is very similar to the previous advisory track, and lies near or slightly to the right of the tightly packed simple- and corrected-consensus track models.

The improved inner-core convective structure argues for at least some slight strengthening during the next couple of days despite the expected 20-21-deg-C sea-surface temperatures (SST) beneath the cyclone. Some cooling aloft associated with the aforementioned second upper-level trough may help to offset the negative effects of the relatively cool SSTs on day 3. In the 96-120-h period, Wanda is expected to interact, and eventually merge, with a cold front and become an extratropical low pressure system with gale-force winds. The new official intensity forecast is very similar to the previous advisory, and closely follows a blend of the intensity consensus models IVCN, NOAA-HCCA, and Florida State FSSE.

FORECAST POSITIONS AND MAX WINDS
 
INIT  03/2100Z 39.8N  39.5W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 12H  04/0600Z 41.0N  39.4W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 24H  04/1800Z 41.9N  39.1W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 36H  05/0600Z 41.8N  38.0W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 48H  05/1800Z 40.3N  37.0W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 60H  06/0600Z 38.8N  36.9W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 72H  06/1800Z 38.1N  36.6W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 96H  07/1800Z 42.4N  31.5W   45 KT  50 MPH - Post Tropical (WNW Fisterra,Spain)
120H  08/1800Z 51.5N  19.2W   45 KT  50 MPH - Post Tropical (WSW Dingle,Ireland)

NWS National Hurricane Center Miami FL 300 PM GMT Wed Nov 03, 2021 

Wanda appears well organized this morning, with visible satellite imagery indicating cyclonically curved convective bands wrapping practically all the way around the circulation center. However, the cloud top temperatures associated with this activity are not very cold, peaking between minus 50 to 55 C in the deepest convection. An ASCAT-A scatterometer pass at 1021 UTC also did not show much change in the peak derived winds (39-kt), although the 34-kt radii have expanded a bit. Subjective Dvorak satellite estimates this morning also remain unchanged at CI 2.5/35 kt from TAFB and CI 3.0/45 kt from SAB. The current intensity is held at 45 kt for this advisory, assuming some undersampling in the scatterometer data.

The storm is moving a little faster to the north-northeast at 015/9 kt. The short-term track philosophy is fairly straightforward, as Wanda continues to be steered generally northward by a narrow mid-level ridge centered to the east of the cyclone. The track guidance remains in good agreement on this evolution over the next 24 hours. Thereafter, the spread in track solutions increases quite dramatically, owing to uncertainty related to the degree of influence an approaching shortwave trough to the north has on Wanda. For now, both the deterministic ECMWF and GFS solutions show this shortwave trough bypassing the cyclone to the north, and in its wake a narrow but sharp mid-level ridge develops west of Wanda, resulting in the cyclone being steered back southward between 48-72 hours. However, the spread in track solutions from both the GFS and ECMWF ensemble members is very large at this time frame. In fact, the 06z GFS ensemble track spread at 60 h is more than 500 n mi, far greater than the average forecast track errors for that period. Finally, a stronger shortwave trough is expected to pick up Wanda in the latter portion of the forecast period, resulting in an abrupt acceleration to the northeast. The official track forecast is similar to the previous one for the first 24 hours, but has been nudged a little south between 48-72 h following the consensus aids. Given the high spread of ensemble solutions beyond 36 h, the track forecast beyond that time is of low confidence.

While Wanda’s winds have not increased over the past 24 hours, its structure on satellite imagery has improved, with convective banding wrapping around the low-level center, aided by low vertical wind shear over the system. Even though Wanda is over marginally warm sea-surface temperatures (SSTs) that decrease further along the track over the next 36 hours, this negative factor will be offset by cooling upper-level temperatures overhead. The trough forecast to bypass Wanda to the north could also provide a bit of baroclinic enhancement aiding ascent over the cyclone. Most of the intensity guidance responds to this environment by showing some slight strengthening and the latest NHC forecast now shows a peak intensity of 50 kt in the 36-48 h time-frame. Afterwards, some increase in shear and decreasing mid-level moisture may lead to weakening, though this could be offset by Wanda moving back over warmer SSTs as it tracks back south. The official intensity forecast is a bit higher than the previous one, but ultimately still shows Wanda losing tropical characteristics by the end of the forecast period as it merges with an approaching mid-latitude trough.

FORECAST POSITIONS AND MAX WINDS

INIT  03/1500Z 38.8N  39.8W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 12H  04/0000Z 40.1N  39.7W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 24H  04/1200Z 41.4N  39.6W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 36H  05/0000Z 41.9N  38.9W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 48H  05/1200Z 40.9N  37.5W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 60H  06/0000Z 39.2N  36.6W   45 KT  50 MPH - Tropical Storm (WNW Fisterra,Spain)
 72H  06/1200Z 38.1N  36.6W   45 KT  50 MPH - Tropical Storm (WNW Fisterra,Spain)
 96H  07/1200Z 40.1N  33.2W   45 KT  50 MPH - Post Tropical (WNW Fisterra,Spain)
120H  08/1200Z 47.1N  27.1W   45 KT  50 MPH - Post Tropical (WNW Fisterra,Spain)

NWS National Hurricane Center Miami FL 900 PM GMT Tue Nov 02, 2021

Late-arriving 1201 UTC ASCAT-B scatterometer data indicated that a small patch of 40-kt winds was located about 30 nmi east and southeast of the well-defined center. Owing to known undersampling by the scatterometer instrument for tropical cyclones that possess a small radius of maximum of winds (RMW), those 40-kt winds support the previous advisory intensity of 45 kt. That 45-kt intensity estimate has been maintained for this advisory based on Wanda having developed a small, closed eye-like feature in shallow convection, with a curved band of deeper convection having recently developed in the RMW where those 40-kt ASCAT surface winds were detected. Wanda’s overall convective organization has improved with more and tighter curved low-level cloud lines now evident in visible satellite imagery.

The initial motion estimate is northward, or 010/07 kt. There remain no significant changes to the previous forecast track or reasoning through 60 h. Thereafter, however, the latest model guidance has made a significant southward shift in the track on days 3-5. For the next couple of days, Wanda is forecast to move slowly poleward ahead of an approaching mid- to upper-tropospheric trough. As the trough weakens and lifts out to the north of the cyclone on day 3, Wanda is expected to move slowly eastward before being forced southeastward to southward by a narrow shortwave ridge that is forecast to trail the aforementioned trough. The GFS and UKMET models show Wanda merging with a frontal system on day 4 and lifting out to the northeast, whereas the ECMWF drives the cyclone farther south ahead of the cold front and turns the system into a convective-free post-tropical cyclone on day 5. For now, the official track forecast remains similar to the previous advisory track through 60 h, and then shows Wanda turning sharply southeastward on day 4, which is well to the right of the previous forecast track. The cyclone is then forecast to lift out to the northeast on day 5 as an extratropical low pressure system after merging with a cold front. The official forecast track is similar to the tightly packed consensus models through 60 h, and then is to the left or north of the consensus aids in the 72-120-h period. There is lower-than-normal confidence in the forecast track after 72 h due to the major difference between the GFS and ECMWF model solutions.

Wanda’s robust low-level circulation should be able to continue to mix out occasional dry air intrusions, allowing for inner-core convection to redevelop and resultant slight strengthening to occur during the next 24-48 h. However, if a band of moderate convection ends up developing around the aforementioned eye-like feature, then Wanda could strengthen a little more than currently forecast. By day 3 and beyond, slow weakening is expected due to a sharp increase in vertical wind shear and a decrease in mid-level moisture. Based on what now appears to be stronger baroclinic forcing in the 60-96-h period, the status of Wanda has been changed to a tropical cyclone on day 3, with the day 4 and 5 statuses indicating extratropical transition due to merger with a frontal system. The new NHC intensity forecast is basically just an update of the previous advisory forecast, and remains close to an average of the intensity consensus models IVCN, NOAA-HCCA, and FSSE.

FORECAST POSITIONS AND MAX WINDS
 
INIT  02/2100Z 36.6N  40.4W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 12H  03/0600Z 37.9N  40.0W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 24H  03/1800Z 39.5N  39.8W   50 KT  60 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 36H  04/0600Z 41.1N  39.7W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 48H  04/1800Z 41.8N  39.4W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 60H  05/0600Z 41.8N  38.0W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 72H  05/1800Z 40.0N  37.5W   45 KT  50 MPH - Tropical Storm (WNW Fisterra, Spain)
 96H  06/1800Z 39.0N  36.0W   45 KT  50 MPH - Post Tropical (WNW Fisterra, Spain)
120H  07/1800Z 43.0N  29.5W   40 KT  45 MPH - Post Tropical (WNW Fisterra, Spain)

NWS National Hurricane Center Miami FL 300 PM GMT Tue Nov 02, 2021 

After the overnight burst of deep convection and associated improved organization, dry air has wrapped into the system from all quadrants and has temporarily eroded Wanda’s inner-core convection. Despite the recent convective degradation, visible satellite imagery indicates that the cyclone’s low-level circulation has improved, with well-defined, curved low-level cloud lines and shallow convection having become more evident. Based on improved low-level structure, the intensity estimate remains at 45 kt despite the overall loss of deep convection.

During the past 6 h, Wanda has made the expected sharp left-hand turn and is now moving northward, or 010/08 kt. There are no significant changes to the previous forecast track or reasoning. Over the next couple of days, the latest model guidance is in excellent agreement that Wanda should remain embedded within a deep-layer trough, and gradually turn toward the north-northeast later today, followed by a northeastward motion tonight and Wednesday as the cyclone moves through the trough-to-ridge flow pattern. By 48-60 hours, the cyclone is forecast to move toward the east and east-southeast as a ridge builds to the northwest and west of Wanda. The new NHC official forecast track is very similar to the previous advisory track, and lies close to the middle of the simple- and corrected-consensus guidance envelope.

The aforementioned improved low-level structure should act to force new convection later today and especially tonight during the nocturnal convective maximum period. Thus, Wanda has another 24-36 h to strengthen while the system remains over marginally warm sea-surface temperatures (SST) near 23 deg C and within a relatively low vertical wind shear environment. Thereafter, slow but steady weakening is likely due to an increase in southwesterly wind shear, a decrease in mid-tropospheric moisture, and a decrease in SSTs. However, baroclinic effects associated with an approaching mid-tropospheric trough from the west could partially offset the weakening process. Wanda is expected become a post-tropical cyclone around 72 h, but this could be delayed if the baroclinic forcing on day 3 ends up stronger than currently expected. The new official intensity forecast is essentially just an update of the previous intensity forecast, and is close to an average of the intensity consensus models IVCN, NOAA-HCCA, and FSSE.

FORECAST POSITIONS AND MAX WINDS

INIT  02/1500Z 35.6N  40.6W   45 KT  50 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 12H  03/0000Z 37.0N  40.0W   45 KT  50 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 24H  03/1200Z 38.8N  39.6W   50 KT  60 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 36H  04/0000Z 40.7N  39.5W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 48H  04/1200Z 42.1N  39.3W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 60H  05/0000Z 42.7N  38.1W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 72H  05/1200Z 42.5N  36.1W   45 KT  50 MPH - Post Tropical (WNW Vila do Corvo,Azores)
 96H  06/1200Z 41.0N  33.0W   45 KT  50 MPH - Post Tropical (WNW Vila do Corvo,Azores)
120H  07/1200Z 42.5N  29.5W   40 KT  45 MPH - Post Tropical (WSW Vigo, Spain)

NWS National Hurricane Center Miami FL 900 PM GMT Mon Nov 01 2021

Wanda is now moving east-northeastward and, as a result, has moved to the east of the upper-level trough axis, while the parent upper-low has detached and pulled out to the north. As a result, Wanda has now made the transition from a subtropical cyclone to a tropical cyclone. This meteorological metamorphosis has been confirmed by ASCAT data from 1200-1300 UTC that showed Wanda now has a small radius of maximum winds (RMW) of 30-35 nmi, and that the outer wind field has weakened and also contracted in size. The intensity is being held at 40 kt based on the earlier ASCAT data showing winds of 33-34 kt, and assuming that there is undersampling owing to the relatively large footprint/resolution of the scatterometer instrument.

The initial motion estimate is 070/06 kt. A complex steering flow pattern is forecast to evolve across the northern Atlantic during the next several days as a series of troughs and ridges in the mid-latitude westerlies pass over and to the north of Wanda. This will cause Wanda to make a zig-zag track across the north-central Atlantic, moving poleward ahead of the troughs and equatorward ahead of the ridges, resulting in a net eastward propagation toward the western Azores. The latest NHC model guidance is in fairly good agreement on the forecast track through day 3, but then diverge on days 4 and 5, with the GFS and ECMWF taking the cyclone more southward closer to the Azores and the remaining dynamical models lifting out Wanda to the north of the Azores. The new NHC official track forecast is similar to the previous advisory track, and follows a blend of the GFEX (GFS-ECMWF) and TVCA simple-consensus models.

Some slight restrengthening will be possible during the next 48 h or so due to a significant decrease in the deep-layer vertical wind shear while Wanda moves over slightly warmer sea-surface temperatures (SST) near 24 deg C. By 96-120 h, Wanda is forecast to devolve into a post-tropical cyclone due to the unfavorable combination of sub-20-deg-C SSTs, a significantly drier air mass, and strong southerly wind shear in excess of 30 kt. The new NHC intensity forecast remains unchanged from the previous advisory and is basically in the middle of the tightly packed intensity guidance suite.

FORECAST POSITIONS AND MAX WINDS
 
INIT  01/2100Z 34.2N  42.2W   40 KT  45 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 12H  02/0600Z 34.7N  41.3W   45 KT  50 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 24H  02/1800Z 36.0N  40.4W   45 KT  50 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 36H  03/0600Z 37.8N  40.0W   45 KT  50 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 48H  03/1800Z 39.9N  39.7W   45 KT  50 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 60H  04/0600Z 41.7N  39.4W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores
 72H  04/1800Z 42.8N  38.3W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 96H  05/1800Z 43.4N  33.3W   45 KT  50 MPH - Post Tropical (WNW Vila do Corvo,Azores)
120H  06/1800Z 42.5N  31.0W   40 KT  45 MPH - Post Tropical (WNW Vila do Corvo,Azores)

NWS National Hurricane Center Miami FL 300 PM GMT Mon Nov 01, 2021 

Wanda has been moving southeastward since the previous advisory and has now moved back underneath the axis of the upper-level trough that the cyclone is embedded in. However, strong northwesterly vertical wind shear of 30-35 kt has persisted and has displaced the deep convection into the southeastern quadrant. The initial intensity has been lowered to 40 kt based on a blend of satellite intensity estimates of 35 kt from TAFB, and 39 kt and 41 kt from UW-CIMSS ADT and SATCON, respectively.

Although Wanda had been moving southeastward at 10-11 kt as of 1200 UTC, the most recent motion vector appears to be slowly eastward or 090/05 kt. Wanda and the parent upper-level trough should move eastward this late morning and early afternoon, and then turn northeastward by this evening, followed by a northward motion by late Tuesday as southerly steering flow gradually develops between a larger mid-latitude trough to the west and a ridge to the east. By day 3, another mid-latitude ridge is forecast to build between Wanda and the aforementioned larger trough, causing the cyclone to turn eastward and then southward toward the westernmost Azores. The latest NHC track guidance has shifted sharply to the east of the previous forecast track through 72 hours, and the new official track forecast has followed suit. However, the new advisory track lies along the western edge of the guidance through day 3, and then lies in the middle of the track guidance envelope on days 4 and 5.

Although Wanda has weakened slightly, some slight restrengthening will be possible in the 24-60-h period when the shear is forecast to decrease sharply down to around 10 kt while the cyclone remains over 23.5-24-deg-C sea-surface temperatures. The weaker shear conditions should also help Wanda transition to a tropical cyclone. By 96 h, however, Wanda is forecast to devolve into a post-tropical low due to the cyclone moving over sub-20-deg-C water temperatures, into a significantly drier air mass, and into strong southerly vertical wind shear — a detrimental combination that should cause the convection to erode near the center. The new NHC intensity forecast is essentially unchanged from the previous advisory.

FORECAST POSITIONS AND MAX WINDS

INIT  01/1500Z 34.0N  43.0W   40 KT  45 MPH - Subtropical (ENE St.Georges,Bermuda)
 12H  02/0000Z 34.1N  42.0W   40 KT  45 MPH - Subtropical (ENE St.Georges,Bermuda)
 24H  02/1200Z 35.0N  41.1W   45 KT  50 MPH - Tropical Storm (ENE St.Georges,Bermuda)
 36H  03/0000Z 36.8N  40.2W   45 KT  50 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 48H  03/1200Z 39.0N  40.0W   45 KT  50 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 60H  04/0000Z 40.8N  39.7W   45 KT  50 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 72H  04/1200Z 42.3N  39.0W   45 KT  50 MPH - Tropical Storm (WNW Vila do Corvo,Azores)
 96H  05/1200Z 43.6N  34.0W   45 KT  50 MPH - Post Tropical (WNW Vila do Corvo,Azores)
120H  06/1200Z 42.9N  31.5W   40 KT  45 MPH - Post Tropical (WNW Vila do Corvo,Azores)

NWS National Hurricane Center Miami FL 900 PM GMT Sun Oct 31, 2021

Wanda has struggled a bit this afternoon, as it appears that some dry air has entrained into its circulation. Deep convection is now mainly confined to a band wrapping around the eastern semicircle of the cyclone. Remarkably, the 3 ASCAT overpasses today missed the core of Wanda, however, the latest Dvorak intensity estimates from TAFB, and the UW-CIMMS ADT and SATCON remain consistent, and indicate an initial advisory intensity of 45 kt.

The storm made a rather abrupt halt in its eastward motion this morning, and for much of the day has been drifting westward, with an initial motion of 90/1 kt. Wanda is expected to make a slow, nearly 180 degree turn to the south, east, then northeast through Tuesday as it pivots around a mid-tropospheric trough. A faster northeast to north motion is expected through Wednesday as ridging builds to the east of the cyclone. The model guidance is in reasonable agreement on this scenario, and there were only minor tweaks to this portion of the NHC track forecast. Thereafter, the guidance has made quite a startling change from the previous runs, and is now indicating that a blocking ridge may build to the north of Wanda by late this week. This is a major shift in the guidance from previous runs that showed the cyclone accelerating northeastward into the mid-latitudes. The latest NHC track forecast tries to adjust for this change by indicating a slower forward speed and less poleward motion late in the 5-day forecast period, but this remains well north and east of the bulk of the guidance. There is also a large amount of spread now in the guidance beyond 72 h, and therefore, that portion of the track forecast is of low confidence.

The upper-trough supporting the subtropical nature of Wanda is forecast to lift out to the northeast by Monday. In addition, over the past day or so, with each passing advisory cycle the cyclone has taken on a little more of the appearance of a tropical cyclone versus a subtropical cyclone. Model guidance is in good agreement on this transition occurring soon, as per the latest FSU phase space forecasts. Therefore, Wanda is expected to transition to a tropical cyclone by Monday. The recent ingestion of dry air may have ended the chance for further strengthening of the storm, and the latest NHC intensity forecast shows no change in strength over the next few days. Beyond 72 h, the intensity forecast becomes murky as there is now a high level of uncertainty as to where Wanda may be headed later this week. The previous NHC forecast had the cyclone moving over much cooler waters late this week. However, the latest shift in the track guidance suggests the cyclone could remain over the current 24 degrees C waters throughout the next 5 days. Regardless of the differing tracks and resulting sea surface temperatures below, the cold pool of air in the upper troposphere that has been giving Wanda a chance to maintain its deep convection will begin to vanish by midweek, therefore, weakening is indicated in the official NHC intensity forecast. The latest NHC intensity forecast was decreased slightly from the previous one, and is close to the various intensity consensus solutions.

FORECAST POSITIONS AND MAX WINDS

INIT  31/2100Z 36.3N  43.2W   45 KT  50 MPH - Subtropical (ENE St.Georges,Bermuda)
 12H  01/0600Z 35.7N  43.0W   45 KT  50 MPH - Subtropical (ENE St.Georges,Bermuda)
 24H  01/1800Z 35.2N  42.2W   45 KT  50 MPH - Tropical Storm (ENE St.Georges,Bermuda)
 36H  02/0600Z 35.6N  41.1W   45 KT  50 MPH - Tropical Storm (ENE St.Georges,Bermuda)
 48H  02/1800Z 36.8N  40.2W   45 KT  50 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 60H  03/0600Z 38.6N  39.7W   45 KT  50 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 72H  03/1800Z 40.7N  39.4W   45 KT  50 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 96H  04/1800Z 44.1N  37.0W   45 KT  50 MPH - Tropical Storm (ENE Vila do Corvo,Azores)
120H  05/1800Z 45.4N  32.0W   40 KT  45 MPH - Post Tropical (WSW Brest,France)

NWS National Hurricane Center Miami FL 300 PM GMT Sun Oct 31, 2021

Wanda is gradually taking on characteristics of a symmetric warm-core cyclone, with bands of organized convection now located across both the northern and southeastern portions of the circulation. The 500-mb heights are slowing rising, while some cirrus outflow is becoming evident to the north of the cyclone. Although Wanda is still considered a subtropical storm due to the presence of the surrounding baroclinic circulation and upper-trough, the baroclinic circulation has been getting more detached from the storm over time. Even though the convective structure continues to evolve, this convection has not been able to become more concentrated near the system’s core since last night. Therefore, the initial advisory intensity remains 45 kt, which is consistent with the latest average of the satellite intensity estimates from TAFB, and UW-CIMSS ADT and SATCON.

The storm has slowed its forward motion and is now moving at 100/07 kt. A turn to the southeast is expected today as Wanda wobbles within the upper-level tropospheric trough that it is embedded within. The upper-trough is forecast to lift out on Monday, leaving Wanda within the weak steering flow near a cutoff mid-level trough. By Tuesday, a ridge is forecast to build to the east of the cyclone, resulting in a turn to the northeast or north, along with an increase in forward speed. By late this week, Wanda should accelerate northeastward within the southwesterly mid-latitude flow. The model guidance is in good agreement on this track scenario, and the latest NHC track forecast is very similar to the previous one.

Despite being over sea surface temperatures below the ideal warmth to support a classic tropical cyclone, the colder-than-typical upper tropospheric temperatures over Wanda should continue to help support deep convection for the next few days. Therefore, some slight strengthening is possible during that time. As mentioned above, the upper-trough is expected to leave Wanda behind by Monday, which should allow the cyclone to complete a tropical transition by that time. Various global model solutions within the Florida State University cyclone phase evolution forecasts agree with this scenario taking place over the next 24 h. After 72 h, decreasing water temperatures in the path of Wanda should cause the cyclone to weaken and become post-tropical by the end of the 5-day forecast period. The latest NHC intensity forecast is unchanged from the previous one, with the only change being the tropical phase of Wanda beginning Monday.

FORECAST POSITIONS AND MAX WINDS

INIT  31/1500Z 36.4N  43.2W   45 KT  50 MPH - Subtropical (ENE St.Georges,Bermuda)
 12H  01/0000Z 35.9N  42.8W   50 KT  60 MPH - Subtropical (ENE St.Georges,Bermuda)
 24H  01/1200Z 34.9N  42.4W   50 KT  60 MPH - Tropical Storm (ENE St.Georges,Bermuda)
 36H  02/0000Z 34.8N  41.2W   50 KT  60 MPH - Tropical Storm (ENE St.Georges,Bermuda)
 48H  02/1200Z 35.6N  40.0W   50 KT  60 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 60H  03/0000Z 37.4N  39.1W   50 KT  60 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 72H  03/1200Z 39.4N  38.7W   45 KT  50 MPH - Tropical Storm (WSW Vila do Corvo,Azores)
 96H  04/1200Z 43.4N  37.3W   45 KT  50 MPH - Tropical Storm (ENE Vila do Corvo,Azores)
120H  05/1200Z 47.2N  30.0W   40 KT  45 MPH - Post Tropical (WSW Brest,France)

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Video: Tropical Storm Wanda November 5, 2021