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Tropical Storm ARTHUR Forecast Discussion Number 4
2014-07-01 22:53:10| National Hurricane Center (Atlantic)
Issued at 500 PM EDT TUE JUL 01 2014 000 WTNT41 KNHC 012053 TCDAT1 TROPICAL STORM ARTHUR DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL012014 500 PM EDT TUE JUL 01 2014 Although radar and satellite imagery indicate that the convective pattern of Arthur has changed little since the previous advisory... an Air Force Reserve reconnaissance aircraft investigating the cyclone this afternoon has found that flight-level and SFMR surface winds in the southeastern quadrant that support increasing the intensity to 45 kt. In fact, the flight crew has been been bounced around pretty good by strong thunderstorms in that area and have been forced to climb to a higher altitude in order to avoid significant turbulence. Arthur has been drifting northwestward at 325/02 kt. No significant change has been made to the previous forecast track or reasoning. The latest reliable numerical models remain in good agreement on large mid-level trough digging southeastward into the northeastern and mid-Atlantic states during the next 72 hours, while a subtropical ridge east of the Carolinas gradually strengthens. The combination of these two systems is expected to steadily increase the southwesterly steering flow over the southeastern United States and the extreme western Atlantic. By Days 4 and 5, Arthur is forecast to accelerate rapidly northeastward ahead of the aforementioned trough as an extratropical cyclone. The official forecast track is again just an update of the previous advisory track, and remains in the middle of the tightly packed guidance envelope and close to the consensus model TVCA. Northwesterly vertical wind shear is expected to gradually abate over the next 48 hours, allowing Arthur to develop an upper-level outflow pattern that is conducive to strengthening. The primary inhibiting factor will be the occasional intrusions of dry mid-level air to the north of the cyclone penetrating into the center and briefly disrupting the inner-core convection. However, the global and regional models are forecasting the inner core region to moisten significantly by 36-48 hours, which should allow Arthur to strengthen into a hurricane while the cyclone is over warm SSTs and in light shear conditions. After 72 hours, Arthur will be be moving over cooler water and is forecast to experience vertical wind shear in excess of 30 kt, which should induce at least steady weakening. The NHC intensity forecast closely follows the consensus model IVCN. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 27.8N 79.4W 45 KT 50 MPH 12H 02/0600Z 28.3N 79.4W 50 KT 60 MPH 24H 02/1800Z 29.2N 79.5W 55 KT 65 MPH 36H 03/0600Z 30.4N 79.2W 60 KT 70 MPH 48H 03/1800Z 32.1N 78.3W 70 KT 80 MPH 72H 04/1800Z 36.6N 73.6W 80 KT 90 MPH 96H 05/1800Z 42.2N 65.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 06/1800Z 46.8N 57.5W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart
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