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Tropical Storm ANA Forecast Discussion Number 6
2015-05-09 10:52:00| National Hurricane Center (Atlantic)
Issued at 500 AM EDT SAT MAY 09 2015 000 WTNT41 KNHC 090851 TCDAT1 TROPICAL STORM ANA DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL012015 500 AM EDT SAT MAY 09 2015 Satellite and NOAA Doppler radar data indicate that Ana has likely made the transition to a tropical cyclone based on the rapid decay of a previously persistent band of outer convection, recent development of inner-core convection within 30-40 nmi of the center, and weak anticyclonic outflow. Between 0500-0700 UTC, average Doppler velocities of 58-60 kt with isolated peak values of 63 kt were noted between 8,000-10,000 ft and within 30-40 dBZ echoes, which would correspond to about 53-54 kt surface winds. However, since that time, that outer band has weakened considerably, so the initial intensity will remain at 50 kt for this advisory. The initial motion estimate using a 12-hour motion is 340/03 kt. There is no significant change to the previous forecast track or reasoning. The global and regional models are in very good agreement that Tropical Storm Ana will move slowly toward the north-northwest or northwest for the next 36 hours or so, followed by a gradual turn toward the north and northeast ahead of an approaching deep-layer trough. By 72 hours, Ana is expected to become extratropical and be absorbed by a much larger extratropical low pressure system by 96 hours. The official track forecast is similar to the previous advisory and lies close to the multi-model consensus TVCN. The center and inner-core region of Ana currently lie along the axis of warmest Gulf Stream water of about 25C. Although inner-core convection has been developing during the past few hours, it is occurring in a region where the last recon flight only found winds of 30-40 kt at the surface and around 45 kt at flight-level. As a result, there could be some fluctuations in Ana's intensity in the near term this morning. By 12-24 hours, the cyclone's slow forward speed will take it over much cooler shelf waters. The combination of SSTs around 20C-22C and continued entrainment of mid-level dry air should induce at least slow weakening until landfall occurs. Although inland at 36 and 48 hours, the intensity has been held up slightly in anticipation of a band of stronger winds lying just offshore. The official intensity forecast is similar to the intensity consensus model ICON. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 32.4N 77.6W 50 KT 60 MPH 12H 09/1800Z 32.8N 77.9W 45 KT 50 MPH 24H 10/0600Z 33.5N 78.4W 40 KT 45 MPH 36H 10/1800Z 34.3N 78.6W 35 KT 40 MPH...INLAND 48H 11/0600Z 35.2N 78.0W 30 KT 35 MPH...INLAND 72H 12/0600Z 39.0N 73.9W 30 KT 35 MPH...POST-TROP/EXTRATROP 96H 13/0600Z...ABSORBED BY LARGER EXTRATROPICAL LOW $$ Forecaster Stewart
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