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Tropical Storm SEYMOUR Forecast Discussion Number 5
2016-10-24 10:53:57| National Hurricane Center (East Pacific)
Issued at 300 AM MDT MON OCT 24 2016 000 WTPZ45 KNHC 240853 TCDEP5 TROPICAL STORM SEYMOUR DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP202016 300 AM MDT MON OCT 24 2016 Seymour continues to strengthen this morning. Satellite data indicate that the banding features have continued to improve and a small central dense overcast feature has developed and become more symmetric. Although earlier microwave imagery revealed a mid-level eye feature, there has been no recent microwave data to diagnose the structure of the inner core. Subjective and objective Dvorak intensity estimates have increased to 55 and 65 kt, respectively, and as a result the initial intensity has been raised to 55 kt. Seymour continues to move west-northwestward at about 13 kt. There has been no change to the track forecast reasoning from the previous advisory. Seymour should continue moving west-northwestward to the south of a deep-layer ridge that extends westward from Mexico. In a couple of days, the cyclone will approach the western portion of the ridge and Seymour should respond by turning northwestward. After 72 hours, an approaching shortwave trough should steer Seymour northward, then northeastward. The model guidance is in good agreement through the first 3 days, but after that time there is more spread in the track models this cycle. The ECMWF and UKMET models have trended faster and take Seymour much farther north at 96 h and 120 h than the remainder of the guidance. Since Seymour is expected to rapidly weaken and become an increasingly shallow system, the NHC forecast leans toward the slower and more southern solutions late in the forecast period. Seymour is forecast to traverse very warm water and remain within an environment of low vertical wind shear and high mid-level moisture during the next day or two. These conditions should allow the cyclone to quickly strengthen during the next 24 to 36 hours and like the previous advisory, the new NHC intensity forecast calls for rapid strengthening during the next 24 hours. In fact, the SHIPS Rapid Intensification Index gives a 78 percent chance of a 30 kt or more increase in wind speed during the next 24 hours. The updated NHC intensity forecast now shows a peak intensity of 100 kt in 48 hours, which is slightly below the LGEM, FSSE, and NOAA corrected consensus (HCCA) models. After 72 hours, increasing southwesterly shear and cooler SSTs are expected to cause a rapid spin down of the tropical cyclone. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 14.9N 108.5W 55 KT 65 MPH 12H 24/1800Z 15.4N 110.5W 70 KT 80 MPH 24H 25/0600Z 16.0N 113.2W 85 KT 100 MPH 36H 25/1800Z 16.4N 115.6W 95 KT 110 MPH 48H 26/0600Z 17.0N 117.9W 100 KT 115 MPH 72H 27/0600Z 19.6N 121.1W 85 KT 100 MPH 96H 28/0600Z 23.0N 121.3W 55 KT 65 MPH 120H 29/0600Z 24.5N 120.0W 30 KT 35 MPH $$ Forecaster Brown
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