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Tropical Storm SIMON Forecast Discussion Number 9
2014-10-03 22:41:32| National Hurricane Center (East Pacific)
Issued at 200 PM PDT FRI OCT 03 2014 000 WTPZ44 KNHC 032041 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 200 PM PDT FRI OCT 03 2014 Recent visible imagery shows that Simon is getting better organized, with the inner core convection now wrapping around the center. In addition, a recent TRMM overpass shows a well-defined low-level circulation center, and a recent ASCAT overpass shows a few vectors of 50-55 kt. Satellite intensity estimates from TAFB and SAB are 55 kt, and that will be the initial intensity. The initial motion is 285/8. Simon should move generally west- northwestward for the next 24-36 hours as it is steered by the subtropical ridge to the north and northeast. After that time, the track guidance remains very divergent. The GFS, GFS ensemble mean, and GFDL forecast Simon to recurve through a break in the ridge near 116W-117W and move inland over the Baja California peninsula and northwestern Mexico. The GFS has shifted somewhat westward since the last advisory, but this did not change its forecast scenario. The ECMWF, NAVGEM, and Canadian models show Simon moving farther west, with a northward turn delayed until the cyclone is near 120W. The ECMWF and Canadian subsequently show Simon dissipating over water. Overall, the guidance envelope has shifted a little to the west at 48-120 hours since the last advisory, and the official forecast does as well. The new forecast lies between the TVCE consensus and the Florida State Superensemble from 48-120 hours, but is notably slower than both of those models. Simon will be moving over warmer water with SSTs near 28-29C while the deep-layer vertical shear is expected to be light. This should allow continued strengthening until the cyclone encounters cooler waters in about 36 hours. The new intensity forecast has been increased over the previous forecast from 12-96 hours based on current trends and the latest SHIPS model guidance. There remain two major sources of uncertainty in the intensity forecast. The first is that rapid intensification could occur during the next 24 hours or so. Second, how much cool water Simon will encounter is dependent on the track. The GFS/GFS Ensemble Mean/GFDL track would keep the storm over relatively warm water, while the ECMWF/NAVGEM/ Canadian track would take it over much cooler water. The ASCAT data shows that Simon remains a very small cyclone in terms of size, with tropical-storm force winds extending no more than 40 n mi from the center. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 18.8N 110.6W 55 KT 65 MPH 12H 04/0600Z 19.2N 112.2W 65 KT 75 MPH 24H 04/1800Z 20.0N 114.3W 75 KT 85 MPH 36H 05/0600Z 20.9N 115.6W 80 KT 90 MPH 48H 05/1800Z 21.9N 116.4W 80 KT 90 MPH 72H 06/1800Z 23.5N 116.5W 65 KT 75 MPH 96H 07/1800Z 24.5N 116.0W 50 KT 60 MPH 120H 08/1800Z 25.5N 115.5W 35 KT 40 MPH $$ Forecaster Beven
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