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| #1068362 (Received by flhurricane at: 11:09 AM 03.Nov.2021) TCDAT1 Tropical Storm Wanda Discussion Number 15 NWS National Hurricane Center Miami FL AL212021 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 12H 04/0000Z 40.1N 39.7W 45 KT 50 MPH 24H 04/1200Z 41.4N 39.6W 45 KT 50 MPH 36H 05/0000Z 41.9N 38.9W 50 KT 60 MPH 48H 05/1200Z 40.9N 37.5W 50 KT 60 MPH 60H 06/0000Z 39.2N 36.6W 45 KT 50 MPH 72H 06/1200Z 38.1N 36.6W 45 KT 50 MPH 96H 07/1200Z 40.1N 33.2W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 08/1200Z 47.1N 27.1W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Papin |
