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Tropical Storm BERTHA Forecast Discussion Number 9
2014-08-03 04:46:07| National Hurricane Center (Atlantic)
Issued at 1100 PM AST SAT AUG 02 2014 000 WTNT43 KNHC 030245 TCDAT3 TROPICAL STORM BERTHA DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 1100 PM AST SAT AUG 02 2014 While there has been some increase in the coverage of cold convective tops associated with Bertha this evening, the cyclone remains disorganized. Surface observations from the Dominican Republic have not definitively shown a closed circulation, and it is possible that what surface circulation there was has been disrupted by land interaction. We will maintain Bertha as a tropical cyclone for now, but advisories could be discontinued on Sunday if the organization of the system does not improve. The initial intensity remains 40 kt based on rain-adjusted SFMR winds reported by the Air Force Hurricane Hunter aircraft well east of the center prior to 00 UTC. The initial motion estimate of 310/19 is based on a blend of the latest satellite imagery and continuity. The synoptic reasoning for the track forecast remains unchanged. Bertha will continue moving northwestward along the southwestern periphery of the subtropical ridge tonight and Sunday. Then the cyclone will turn northward on Monday between the ridge and a deep-layer trough over the southeastern United States, followed by a northeastward acceleration into the mid-latitude westerlies. The track model guidance remains in good agreement on this general scenario. However, the models have shifted to the left this cycle at 48 hours and beyond, showing a more gradual recurvature. The NHC track through 36 hours is largely an update of the previous one. After that time, the official forecast has been adjusted to the left of the previous one, but now lies along the right side of the guidance envelope. There continue to be three possible scenarios for the intensity of Bertha. The official forecast assumes that Bertha will survive its current lack of structure, land interaction, shear, and dry air entrainment long enough to reach a more favorable environment in 24-36 hours. At that point, the environment would likely allow for intensification until extratropical transition begins after 96 hours. The new NHC intensity forecast is similar to the previous one and calls for Bertha to become a hurricane in 4 days, and is close to the latest IVCN intensity consensus. An alternate scenario is that Bertha degenerates to a tropical wave in the next 12 to 24 hours, with possible regeneration later when the system reaches the more favorable environment. A third possibility involves a trough of low pressure currently situated over the central and northwestern Bahamas. The 1200 UTC runs of the UKMET and NAVGEM forecast the low to absorb Bertha in 48 hours or so, while the latest GFS and ECMWF runs keep this system weaker and maintain Bertha through the forecast period. Later model runs should help refine the likelihood of this scenario. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 19.5N 69.7W 40 KT 45 MPH 12H 03/1200Z 21.5N 71.8W 40 KT 45 MPH 24H 04/0000Z 24.1N 73.8W 45 KT 50 MPH 36H 04/1200Z 27.2N 74.4W 45 KT 50 MPH 48H 05/0000Z 30.4N 73.8W 50 KT 60 MPH 72H 06/0000Z 36.0N 69.0W 60 KT 70 MPH 96H 07/0000Z 41.0N 60.0W 65 KT 75 MPH 120H 08/0000Z 45.0N 50.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Brennan
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