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Tropical Storm SEYMOUR Forecast Discussion Number 4
2016-10-24 04:40:51| National Hurricane Center (East Pacific)
Issued at 900 PM MDT SUN OCT 23 2016 000 WTPZ45 KNHC 240240 TCDEP5 TROPICAL STORM SEYMOUR DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP202016 900 PM MDT SUN OCT 23 2016 Seymour's convective pattern has continued to improve since the previous advisory, with the development of a mid-level eye feature noted in 23/2250Z and 24/0107Z SSMI/S microwave images. Dvorak classifications from TAFB and SAB are T3.0/45 kt and T3.5/55 kt, respectively, and T3.6/57 kt from UW-CIMSS ADT. The initial intensity is set on the low side of these estimates at 45 kt for this advisory, which could be conservative. The initial motion estimate is 290/13 kt. For the next 72 h, the global models remain in excellent agreement on Seymour moving west-northwestward along the southern periphery of a deep-layer ridge located over Mexico. After that, the cyclone is expected to turn northward around the western portion of the ridge and ahead of a shortwave trough forecast to approach Seymour from the northwest by late Wednesday. The official forecast track lies basically down the middle of the guidance envelope, close to the multi-model consensus TVCN. The global and regional models indicate environmental conditions are forecast to be quite favorable for additional strengthening to occur during the next 3 days. In fact, due to a combination of the vertical shear being low at around 5 kt, mid-level humidity values being near 70 percent, sea-surface temperatures expected to be at least 29 deg C, and the recent development of a mid-level eye, a period of rapid intensification is forecast to occur for the next 24 hours. This trend is supported by the SHIPS and LGEM statistical intensity models, and also by the HWRF model and the new NOAA Corrected Consensus Model, HCCA, which makes Seymour a major hurricane by 48 hours. By 72 hours and beyond, increasing southwesterly vertical wind shear ahead of the aforementioned shortwave trough and SSTs less than 25 deg C and are expected to induce rapid weakening. The new intensity forecast lies close to a blend of the SHIPS and LGEM models, which is significantly higher than the previous advisory, but remains well below the peak intensity forecast of 110 kt by HCCA and the 112-kt forecast from the HWRF model. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 14.4N 107.1W 45 KT 50 MPH 12H 24/1200Z 14.9N 109.1W 60 KT 70 MPH 24H 25/0000Z 15.6N 111.7W 75 KT 85 MPH 36H 25/1200Z 16.1N 114.4W 85 KT 100 MPH 48H 26/0000Z 16.7N 116.6W 90 KT 105 MPH 72H 27/0000Z 18.7N 120.2W 90 KT 105 MPH 96H 28/0000Z 22.0N 120.8W 65 KT 75 MPH 120H 29/0000Z 24.0N 120.0W 45 KT 50 MPH $$ Forecaster Stewart
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