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Tropical Storm BERTHA Forecast Discussion Number 5
2014-08-02 04:54:59| National Hurricane Center (Atlantic)
Issued at 1100 PM AST FRI AUG 01 2014 000 WTNT43 KNHC 020254 TCDAT3 TROPICAL STORM BERTHA DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 1100 PM AST FRI AUG 01 2014 While some convection developed near the estimated center during the past few hours, the circulation of Bertha remains disorganized. In fact, the Hurricane Hunter aircraft has been unable to find a center at 5000 ft this evening. However, surface observations suggested that there was still a small closed surface circulation when Bertha moved between Martinique and Dominica a few hours ago. The estimated center position is on the southwestern edge of the convective canopy, consistent with the 16 kt of southwesterly shear analyzed by the SHIPS model. The initial intensity remains 45 kt based on several SFMR winds of 40-45 kt reported by the aircraft east and northeast of the center. While the SHIPS model shows the shear decreasing on Saturday, Bertha will continue moving through a dry environment during the next 24 to 36 hours. There is also the potential for land interaction with Puerto Rico and Hispaniola during this time, which could disrupt the small circulation. Given all of these factors, little change in intensity is expected through 36 hours. After that time, if Bertha survives, the environment is expected to become more favorable for intensification with warming SSTs, increasing moisture, and lower vertical shear. Much of the intensity guidance shows Bertha reaching hurricane strength in 72 to 96 hours, and the official forecast follows suit. The new NHC intensity forecast has been adjusted upward from 48 to 96 hours, but remains a little below the IVCN intensity consensus. Note that it is possible that the combination of shear, dry air, and land interaction could cause Bertha to degenerate to a tropical wave during the next 36 hours, followed by possible regeneration when the system reaches the more favorable environment later in the forecast period. The initial motion estimate is 290/19, as Bertha is being steered west-northwestward by a deep-layer subtropical ridge over the western Atlantic. The ridge will begin to erode after 24 hours as a mid- to upper-level trough moves through the eastern United States, which should allow Bertha to turn northwestward and then northward by 3 days. After that time, Bertha is expected to complete recurvature and accelerate northeastward into the north Atlantic. The track model guidance remains in good agreement on this general scenario, however, there is a fair bit of spread in how sharply Bertha will recurve. The GFS and GEFS ensemble mean lie on the eastern edge of the guidance envelope, with the ECMWF, HWRF, and GFDL showing a more gradual turn and a track a little farther west. Through 36 hours the new NHC track is an update of the previous one. After that time, the official forecast has been nudged toward the left, but lies a little to the right of the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 02/0300Z 15.7N 63.0W 45 KT 50 MPH 12H 02/1200Z 16.9N 65.5W 45 KT 50 MPH 24H 03/0000Z 19.0N 68.6W 45 KT 50 MPH 36H 03/1200Z 21.4N 71.2W 45 KT 50 MPH 48H 04/0000Z 24.0N 73.2W 50 KT 60 MPH 72H 05/0000Z 30.0N 73.5W 60 KT 70 MPH 96H 06/0000Z 35.5N 68.0W 65 KT 75 MPH 120H 07/0000Z 40.0N 59.0W 60 KT 70 MPH $$ Forecaster Brennan
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