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Tropical Storm JOAQUIN Forecast Discussion Number 7
2015-09-29 18:51:00| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT TUE SEP 29 2015 000 WTNT41 KNHC 291650 TCDAT1 TROPICAL STORM JOAQUIN DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112015 ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1100 AM EDT TUE SEP 29 2015 CORRECTED INTENSITY TO 40 KT IN FIRST PARAGRAPH Visible satellite imagery this morning shows that the cloud pattern of the tropical cyclone is somewhat better organized than it was 24 hours ago. The low-level center is situated near the northern side of the main area of deep convection due to northerly shear. The upper level outflow is well defined over the southern semicircle of the system, and restricted over the northern part of the circulation. The current intensity is conservatively set at 40 kt, which is a little below the latest Dvorak estimates. An Air Force plane will be investigating Joaquin in a few hours, and should provide a better estimate of intensity. Based on the satellite center fixes, the initial motion continues to be slowly westward, or 260/04 kt. The forecast track in this advisory attempts to reconcile large model spread with an overall shift toward the southwest of the previous track through 72 hours. Joaquin is currently in a relatively weak steering pattern, but a building shortwave ridge in the northwestern Atlantic should allow the cyclone to drift west and then west-southwestward. This pushes the storm in the direction of the Bahamas, but the deterministic and ensemble model consensus still shows a good likelihood that Joaquin will stop fairly well short of the Bahamas, and then begin accelerating to either the north or northeast. The 00Z ECMWF made a closer approach to the Bahamas, but it too turns the storm sharply and accelerates it back into the Atlantic beyond 72 hours. The official forecast is to the left of the previous forecast through 72 hours, and significantly slower at 4 and 5 days. It should be repeated that the confidence in the track forecast is very low. The vertical shear is predicted by the dynamical models to decrease in 1 to 2 days. This should allow for additional strengthening, which is reflected in the official forecast. The NHC wind speed predictions may be conservative, since some of the guidance suggests that Joaquin could become a hurricane in a few days. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 26.5N 70.8W 40 KT 45 MPH 12H 30/0000Z 26.4N 71.5W 45 KT 50 MPH 24H 30/1200Z 26.3N 72.4W 45 KT 50 MPH 36H 01/0000Z 26.2N 73.1W 50 KT 60 MPH 48H 01/1200Z 26.1N 73.7W 55 KT 65 MPH 72H 02/1200Z 26.0N 74.0W 60 KT 70 MPH 96H 03/1200Z 29.0N 73.5W 60 KT 70 MPH 120H 04/1200Z 34.0N 72.0W 60 KT 70 MPH $$ Forecaster Pasch/Burke
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