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Tropical Storm HENRI Forecast Discussion Number 8
2015-09-10 22:33:38| National Hurricane Center (Atlantic)
Issued at 500 PM AST THU SEP 10 2015 000 WTNT43 KNHC 102033 TCDAT3 TROPICAL STORM HENRI DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082015 500 PM AST THU SEP 10 2015 Henri continues to struggle with most of its deep convection well removed to the northeast of the center. In fact, it is taking on some characteristics of a subtropical cyclone with recent scatterometer data indicating that the radius of maximum winds has increased to a rather high value of 120 n mi. The initial wind speed will remain 35 kt on the basis of 30-35 kt winds observed in partial scatterometer pass that missed the area that likely has the strongest winds. Southerly shear is still forecast to relax overnight near Henri, which theoretically could result in intensification during the next day or so before the cyclone moves over cold water on Saturday. However, dry air aloft persists near the storm and the overall cloud pattern is quite disorganized. The unfavorable factors are starting to outweigh the favorable conditions, so the official intensity forecast is reduced from the previous one, a little below the model consensus. Extratropical transition is expected within 2 days due to strong shear and very cold water. A reasonable alternative solution provided by some of the global models is that the cyclone stays weak and opens up into a trough during the day on Friday. Henri is moving faster to the north, now about 13 kt. The storm should continue to accelerate northward tonight and northeastward tomorrow due to it encountering faster steering from the subtropical ridge. After that time, an even faster northeastward and then eastward motion is predicted when the cyclone becomes embedded in the mid-latitude flow. The guidance has trended to the left with the track of Henri, perhaps due to a weaker forecast representation of the storm. The NHC forecast is shifted in that direction, although remains on the right side of the guidance envelope. If it survives, the cyclone should become absorbed by a larger extratropical low by day 4 over the far North Atlantic. The latter part of this forecast, when the storm is expected to be post-tropical, is based on guidance provided by NOAA's Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 10/2100Z 33.9N 60.7W 35 KT 40 MPH 12H 11/0600Z 36.1N 60.3W 40 KT 45 MPH 24H 11/1800Z 39.7N 59.1W 40 KT 45 MPH 36H 12/0600Z 43.5N 56.5W 40 KT 45 MPH 48H 12/1800Z 46.8N 51.8W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 13/1800Z 48.5N 36.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 14/1800Z...DISSIPATED $$ Forecaster Blake
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