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Tropical Depression SIX Forecast Discussion Number 2
2016-08-17 10:37:41| National Hurricane Center (Atlantic)
Issued at 500 AM AST WED AUG 17 2016 000 WTNT41 KNHC 170837 TCDAT1 TROPICAL DEPRESSION SIX DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 500 AM AST WED AUG 17 2016 The depression's cloud pattern is gradually becoming better organized. It consists of a central mass of deep convection and a newly formed band over the northern half of the circulation. The low-level center appears to still be located near the northeastern edge of the main convective mass, likely due to some northeasterly shear. Satellite classifications are T2.0 from TAFB and SAB, and support maintaining the initial intensity estimate of 30 kt. The northeasterly shear is forecast to decrease while the cyclone moves over marginally warm waters during the next 24 to 36 hours. These two factors should favor some intensification during this time frame. However, the global models, and the ECMWF in particular, show the cyclone moving into a much drier environment after 48 hours and encountering strong southwesterly shear in association with a mid- to upper-level trough. Thus weakening is forecast to begin by day 3 despite the cyclone's trek over warmer waters, and there is the possibility that the system could degenerate into a remnant low by day 4 or 5 as depicted in the ECMWF. The new NHC intensity forecast is somewhat higher than the previous one and the multi- model consensus in the short term but lower later in the forecast period and a little below most of the guidance. The depression has been responding to a weakness in the subtropical ridge between 40w and 50w by moving on a northwesterly track, and the initial motion estimate is 305/13. The track guidance remains split into two distinct camps, with GFS-based deterministic models and GFS ensemble members showing a deeper system moving more poleward. The ECMWF and its ensemble solutions are much farther to the south as a result of the model's forecast of a weaker, shallower system moving on a more westerly course. Based on the assumption of a weaker system, the NHC track forecast is adjusted toward the ECMWF solution, and is well south of the previous one and a little to the left of the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 17/0900Z 13.2N 35.2W 30 KT 35 MPH 12H 17/1800Z 14.3N 36.8W 40 KT 45 MPH 24H 18/0600Z 15.5N 38.3W 45 KT 50 MPH 36H 18/1800Z 16.8N 39.9W 50 KT 60 MPH 48H 19/0600Z 17.8N 41.4W 50 KT 60 MPH 72H 20/0600Z 19.2N 44.7W 45 KT 50 MPH 96H 21/0600Z 21.6N 48.9W 40 KT 45 MPH 120H 22/0600Z 23.6N 52.3W 35 KT 40 MPH $$ Forecaster Kimberlain
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