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Hurricane Gert Forecast Discussion Number 16
2017-08-16 22:33:40| National Hurricane Center (Atlantic)
Issued at 500 PM AST Wed Aug 16 2017 000 WTNT43 KNHC 162033 TCDAT3 Hurricane Gert Discussion Number 16 NWS National Hurricane Center Miami FL AL082017 500 PM AST Wed Aug 16 2017 Cloud tops with temperatures colder than -65 deg C have wrapped almost entirely around Gert's center, although eye temperatures have been fluctuating all day. Dvorak intensity estimates vary widely, from T4.5 from TAFB to around T5.5 from the UW-CIMSS ADT, and since a warm eye has been unable to persist for an extended period of time, the initial intensity is raised conservatively to 85 kt. This makes Gert the first category 2 hurricane of the season. The window of opportunity for additional strengthening appears to be closing. Gert will be moving over the colder waters north of the Gulf Stream in about 12-18 hours, and southwesterly shear will be increasing to well over 30 kt in about 12 hours. Therefore, a fast weakening trend is forecast to begin on Thursday, with Gert becoming a tropical storm by 36 hours. The FSU phase-space diagrams indicate that Gert should be extratropical just after 36 hours, and the GFS, ECMWF, and UKMET all have the cyclone being absorbed by a larger extratropical low over the north Atlantic by day 4. Acceleration continues with the initial motion now 055/27 kt. With Gert firmly embedded within the mid-latitude westerlies, the hurricane's forward speed should increase for the next 24 hours, followed by some deceleration as the cyclone begins to interact with a large cut-off low moving east of Atlantic Canada. Most of the track guidance is a little faster on this cycle, although the ECMWF is significantly slower. The new NHC forecast is nudged a little faster from 12-48 hours, but not too fast given the latest ECMWF solution. The post-tropical portion of the track, intensity, and wind radii forecasts incorporate guidance from NOAA's Ocean Prediction Center. Swells from Gert are affecting portions of the mid-Atlantic coast of the United States, and are expected to spread northward to New England and Atlantic Canada during the next day or two. These swells are likely to produce dangerous surf and rip current conditions. Please consult products from your local weather forecast office for more information. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 38.7N 62.4W 85 KT 100 MPH 12H 17/0600Z 40.7N 56.9W 85 KT 100 MPH 24H 17/1800Z 44.3N 48.2W 70 KT 80 MPH 36H 18/0600Z 48.3N 40.4W 55 KT 65 MPH 48H 18/1800Z 51.6N 35.7W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 19/1800Z 54.3N 32.6W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 20/1800Z...ABSORBED BY A LARGER EXTRATROPICAL LOW $$ Forecaster Berg
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