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Tropical Storm BERTHA Forecast Discussion Number 13
2014-08-04 04:45:28| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT SUN AUG 03 2014 000 WTNT43 KNHC 040245 TCDAT3 TROPICAL STORM BERTHA DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 1100 PM EDT SUN AUG 03 2014 Recent satellite and aircraft reconnaissance data indicate that the circulation of Bertha has become much better defined this evening. The tropical cyclone has also quickly strengthened as convection has increased and become organized in a band around the eastern portion of the circulation. An Air Force reconnaissance aircraft has measured peak believable SFMR winds of around 55 kt. Although the flight-level winds would support a little lower initial intensity, a recent dropsonde measured winds in the lowest 150 meters that also supports an initial wind speed of 55 kt. The aircraft data also indicate that the minimum pressure has fallen to around 1007 mb. The strong northwesterly vertical wind shear that has been affecting Bertha is forecast to decrease further during the next 24 hours. This should allow for additional strengthening, and the updated NHC intensity forecast calls for Bertha to become a hurricane in a day or so. In 36 to 48 hours, strong west-southwesterly upper-level winds are forecast to cause a significant increase in vertical shear. The shear, along with decreasing sea surface temperatures, should cause some weakening before Bertha becomes an extratropical low over the North Atlantic in three to four days. Bertha is moving north-northwest at 15 kt. The cyclone should turn northward and then north-northeastward during the next day or so while it moves between a subtropical high to its east and a mid- to upper-level trough over the eastern United States. In a couple of days, Bertha is expected to accelerate northeastward and then turn east-northeastward when it moves into the mid-latitude westerlies. The model guidance is generally in good agreement on this scenario through 72 hours, and the new NHC track forecast is similar to the previous advisory during that time. There is increasing spread in the track guidance after three days with the ECMWF and UKMET models predicting a much faster motion over the North Atlantic than the latest GFS. The four- and five-day forecast positions are close to the model consensus and guidance provided by the NOAA Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 24.9N 73.2W 55 KT 65 MPH 12H 04/1200Z 27.3N 73.7W 60 KT 70 MPH 24H 05/0000Z 30.8N 73.4W 65 KT 75 MPH 36H 05/1200Z 34.1N 72.0W 65 KT 75 MPH 48H 06/0000Z 36.9N 69.0W 65 KT 75 MPH 72H 07/0000Z 42.2N 59.5W 60 KT 70 MPH 96H 08/0000Z 47.5N 50.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 09/0000Z 49.5N 40.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown
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