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Tropical Storm SIMON Forecast Discussion Number 7
2014-10-03 10:57:54| National Hurricane Center (East Pacific)
Issued at 200 AM PDT FRI OCT 03 2014 000 WTPZ44 KNHC 030857 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 200 AM PDT FRI OCT 03 2014 Microwave satellite images early this morning indicate that the inner-core region of Simon is not particularly well organized. A low-level eye feature has been intermittent since about 0000 UTC, but the most recent images do not show the eye feature any longer. Subjective and objective satellite intensity estimates suggest that Simon has strengthened to 55-60 kt based on a CDO feature. However, two ASCAT overpasses at 0412 UTC and 0504 UTC only indicated surface winds of 39 kt and 41 kt, respectively. Even allowing for some undersampling due to the compact size of the cyclone likely only yields 45-50 kt. Owing to the lack of persistent central features, the initial intensity is being held at 45 kt for this advisory. The initial motion is an uncertain 280/06 kt and is based primarily on microwave satellite fixes. There remains high confidence that Simon will continue to move westward to west-northwestward for the next 2-3 days as the cyclone navigates around the western periphery of a strong deep-layer ridge located north of the cyclone. After that time, however, the model guidance diverges quite significantly. The overwhelming majority of the guidance recurves Simon toward the north by Day 4 and toward the northeast by Day 5. However, the very reliable ECMWF model takes Simon farther west through Day 5 and does not recurve the cyclone until after this forecast period. Owing to the significant differences in the various model solutions, and out of respect for the ECMWF model, and given that mid-level northwesterly flow patterns are not conducive for recurvature scenarios, the official forecast was only nudged a little to the west of the previous forecast track. Simon will be moving over warmer water with SSTs near 28-29C during the next 24-36 hours while the deep-layer vertical shear is light. However, modest easterly mid-level shear that has been undercutting the otherwise impressive outflow pattern may continue to occasionally disrupt the inner core convection before Simon reaches cooler water and a drier, more stable airmass by Days 4 and 5. As a result, only slow steady strengthening is forecast, which is similar to the SHIPS intensity model and the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 18.3N 108.9W 45 KT 50 MPH 12H 03/1800Z 18.7N 110.3W 55 KT 65 MPH 24H 04/0600Z 19.3N 112.2W 65 KT 75 MPH 36H 04/1800Z 20.0N 114.1W 75 KT 85 MPH 48H 05/0600Z 21.0N 115.8W 75 KT 85 MPH 72H 06/0600Z 22.5N 116.5W 60 KT 70 MPH 96H 07/0600Z 24.0N 116.0W 50 KT 60 MPH 120H 08/0600Z 25.0N 115.5W 35 KT 40 MPH $$ Forecaster Stewart
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