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Tropical Storm SIMON Forecast Discussion Number 4
2014-10-02 16:45:21| National Hurricane Center (East Pacific)
Issued at 800 AM PDT THU OCT 02 2014 000 WTPZ44 KNHC 021445 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 800 AM PDT THU OCT 02 2014 First-light visible imagery shows that Simon is gradually becoming better organized. The center is under a ragged central dense overcast, and outer bands are occurring in all quadrants except the north. Satellite intensity estimates from TAFB and SAB are 35 kt, while recent AMSU and SATCON estimates from CIMSS are 35-40 kt. The initial intensity remains 35 kt, but this could be a little conservative. The initial motion is 295/9, and this general motion is expected to continue for the next 2 days or so while the storm is steered by mid-level ridging to its north and northeast. The model guidance is in fair agreement during that time period, and the NHC track forecast remains near the middle of the guidance envelope. The guidance continues to show significant divergence after 48 hours. The GFS, GFDL, and HWRF, show a northeastward turn between 72-120 hours, while the the ECMWF and UKMET show a generally northward motion. In addition, the NAVGEM shows a west-northwestward motion through the entire forecast period. The track forecast compromises between these extremes by showing a slow northward motion by 120 hours. Overall, the new forecast is similar to, but faster than, the previous forecast. However, it is notably slower than the consensus model TVCE from 72-120 hours. Simon is forecast to remain in a light vertical wind shear environment and over sea surface temperatures of 28-29C for the next 48 hours. This should allow at least steady strengthening, and there is an above normal chance for rapid strengthening as shown by the Rapid Intensification Index of the SHIPS model. After 48 hours, the center is expected to move over cooler sea surface temperatures and into an area of westerly shear. These conditions should cause a weakening trend, albeit at a slower rate than seen during Rachel a few days ago. The new intensity forecast is increased above that of the previous forecast and is in best overall agreement with the SHIPS model. FORECAST POSITIONS AND MAX WINDS INIT 02/1500Z 18.4N 107.1W 35 KT 40 MPH 12H 03/0000Z 18.9N 108.4W 40 KT 45 MPH 24H 03/1200Z 19.3N 110.3W 50 KT 60 MPH 36H 04/0000Z 19.8N 112.0W 60 KT 70 MPH 48H 04/1200Z 20.4N 113.5W 70 KT 80 MPH 72H 05/1200Z 22.5N 115.5W 70 KT 80 MPH 96H 06/1200Z 24.0N 115.5W 60 KT 70 MPH 120H 07/1200Z 25.0N 115.5W 45 KT 50 MPH $$ Forecaster Beven
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