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Tropical Storm GRACE Forecast Discussion Number 2
2015-09-05 22:33:03| National Hurricane Center (Atlantic)
Issued at 500 PM AST SAT SEP 05 2015 000 WTNT42 KNHC 052032 TCDAT2 TROPICAL STORM GRACE DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072015 500 PM AST SAT SEP 05 2015 The depression's cloud pattern has gradually increased in organization since the last advisory. A band over the southwestern portion of the circulation has taken more shape, with cloud tops cooling slightly during the last several hours. Microwave and conventional satellite imagery also suggest that some inner-core structural organization has already developed. Dvorak intensity estimates were T2.5/ 35 kt from TAFB and SAB at 1800 UTC, so the initial intensity estimate is 35 kt. Large-scale conditions should be conducive for some intensification during the next 24 to 36 hours, with the depression embedded in an environment of light easterly shear and over warm SSTs. The one caveat is that a general drying of the lower to middle troposphere in the near-storm environment is forecast, possibly due to increasing subsidence, which could squelch additional strengthening. After 48 hours, the cyclone is forecast to encounter westerly flow aloft associated with an enhanced upper-level trough extending from near the Antilles to the eastern tropical Atlantic. This pattern should produce enough vertical shear to cause weakening or possibly even dissipation by day 4 or 5 of the forecast. The new intensity forecast shows slightly greater intensification in the short term relative to the previous one, with a peak in 36 hours, and greater weakening at the end of the forecast. The initial motion estimate is 280/12. A low- to mid-level ridge over the subtropical Atlantic should keep the cyclone on a westward to west-northwestward track throughout the forecast period. The new track forecast is faster than the previous one, especially at the extended range, and on the south side of guidance envelope in best agreement with the FSU Superensemble and ECMWF model solution. This makes intuitive sense, since a weaker system would likely track farther south and move faster. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 12.6N 26.4W 35 KT 40 MPH 12H 06/0600Z 12.9N 28.3W 40 KT 45 MPH 24H 06/1800Z 13.2N 30.8W 45 KT 50 MPH 36H 07/0600Z 13.5N 33.6W 50 KT 60 MPH 48H 07/1800Z 13.9N 36.4W 45 KT 50 MPH 72H 08/1800Z 14.8N 42.3W 45 KT 50 MPH 96H 09/1800Z 15.1N 48.4W 40 KT 45 MPH 120H 10/1800Z 15.7N 53.8W 35 KT 40 MPH $$ Forecaster Kimberlain
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