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Tropical Storm HENRI Forecast Discussion Number 5
2015-09-10 04:45:19| National Hurricane Center (Atlantic)
Issued at 1100 PM AST WED SEP 09 2015 000 WTNT43 KNHC 100244 TCDAT3 TROPICAL STORM HENRI DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082015 1100 PM AST WED SEP 09 2015 Recently received ASCAT-B scatterometer data showed an area of 35-40 kt wind vectors in the convection about 75-100 n mi east of the center. Based on this, the initial intensity is increased to a possibly conservative 35 kt and the cyclone is upgraded to a tropical storm. Despite the upgrade, Henri remains a disorganized system, with the low-level center remaining exposed to the west of the convection due to 15-20 kt of shear. In addition, microwave satellite data and experimental European multispectral satellite imagery suggest a tongue of dry air is entraining into the cyclone around the west, south, and southeast sides of the circulation. Henri has started its expected northward track with the initial motion of 355/4. For the next 36-48 hours, the cyclone should move generally northward with an increase in forward speed between the subtropical ridge to the east and a deep-layer trough moving eastward through the eastern United States. After that time, Henri should turn northeastward and eastward as it enters the westerlies. The new forecast track is similar to the previous track, but it lies a little south of the center of the guidance envelope after 36 hours due to a northward shift in the guidance. The dynamical models suggest that the shear should subside during the next 36-48 hours, and that the dry air entrainment should also decrease. This combination should allow Henri to strengthen until it reaches colder sea surface temperatures north of the Gulf Stream in a little under 48 hours. After that, the cyclone is expected to become extratropical as it merges with a frontal system. The new intensity forecast calls for a peak intensity near 50 kt in 36-48 hours, followed by gradual weakening. The first 48 hours are in best agreement with the SHIPS model, and the intensities after extratropical transition are based on input from the NOAA Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 31.3N 60.7W 35 KT 40 MPH 12H 10/1200Z 32.8N 60.9W 40 KT 45 MPH 24H 11/0000Z 35.3N 60.9W 45 KT 50 MPH 36H 11/1200Z 38.6N 60.2W 50 KT 60 MPH 48H 12/0000Z 42.4N 58.0W 50 KT 60 MPH 72H 13/0000Z 47.5N 48.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 14/0000Z 47.5N 32.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 15/0000Z 47.0N 17.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven
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