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Tropical Depression ELEVEN Forecast Discussion Number 3
2015-09-28 16:51:35| National Hurricane Center (Atlantic)
Issued at 1100 AM AST MON SEP 28 2015 000 WTNT41 KNHC 281451 TCDAT1 TROPICAL DEPRESSION ELEVEN DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112015 1100 AM AST MON SEP 28 2015 Satellite imagery indicates that the depression's overall cloud pattern has become better organized since yesterday despite persistent north- northwesterly shear of about 20 kt. The exposed low-level center is located near the northwestern tip of a curved band over the southeastern quadrant of the circulation. However, satellite data indicate that the low- to mid-level centers have recently become more separated. Dvorak intensity estimates are a consensus T2.0/30 kt from TAFB and SAB, so the initial intensity is held at 30 kt. Smoothing fixes over the last 12 hours yields an initial motion of 300/04, a little faster than before. The depression is embedded in low- to mid-level southeasterly flow around a ridge to its northeast, with northwesterly flow aloft. This synoptic pattern should only favor a slow northwestward motion for the next couple of days. After 48 hours, the cyclone should reach the western end of the low- to mid-level subtropical ridge and begin to respond to the southerly and southwesterly flow ahead of a baroclinic trough nearing the U.S. east coast. This change to the steering should result in a gradual northward turn with increasing forward speed. The new track forecast is a little left of the previous one at 48 hours and a little faster, close to a blend of the GFS and ECWMF model solutions. GFS- and ECMWF-based SHIPS model output indicates a continuation of moderately strong north-northwesterly shear over the cyclone for the next day or so. Even though other large-scale factors are generally conducive for intensification during this time, shear of this magnitude suggests that only slow intensification is possible. While the shear should decrease some by 36 hours, other environmental factors are not forecast to be as conducive and little further strengthening is indicated. Large-scale models depict the cyclone merging with a frontal zone offshore of the Mid-Atlantic or New England coasts by 96 hours, and the system is therefore shown to be post-tropical at that time. An alternate lower probability scenario is that the cyclone could race ahead of the frontal boundary and retain its tropical characteristics for a bit longer. The new intensity forecast is above the previous one through 24 hours and near the multi-model consensus but below the statistical-dynamical guidance after that time due to more reliance on the global models which show little further intensification. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 27.8N 69.6W 30 KT 35 MPH 12H 29/0000Z 28.1N 70.0W 40 KT 45 MPH 24H 29/1200Z 28.5N 70.6W 40 KT 45 MPH 36H 30/0000Z 29.1N 71.4W 40 KT 45 MPH 48H 30/1200Z 29.6N 72.0W 40 KT 45 MPH 72H 01/1200Z 32.0N 72.9W 35 KT 40 MPH 96H 02/1200Z 37.7N 72.9W 35 KT 40 MPH...POST-TROPICAL 120H 03/1200Z...DISSIPATED $$ Forecaster Kimberlain
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