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| #1068005 (Received by flhurricane at: 4:51 PM 31.Oct.2021) TCDAT1 Subtropical Storm Wanda Discussion Number 4 NWS National Hurricane Center Miami FL AL212021 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 12H 01/0600Z 35.7N 43.0W 45 KT 50 MPH 24H 01/1800Z 35.2N 42.2W 45 KT 50 MPH...TROPICAL CYCLONE 36H 02/0600Z 35.6N 41.1W 45 KT 50 MPH 48H 02/1800Z 36.8N 40.2W 45 KT 50 MPH 60H 03/0600Z 38.6N 39.7W 45 KT 50 MPH 72H 03/1800Z 40.7N 39.4W 45 KT 50 MPH 96H 04/1800Z 44.1N 37.0W 45 KT 50 MPH 120H 05/1800Z 45.4N 32.0W 40 KT 45 MPH...POST-TROPICAL $$ Forecaster Latto |
