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Tropical Storm Fernanda Forecast Discussion Number 6
2017-07-13 10:44:38| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Thu Jul 13 2017 000 WTPZ41 KNHC 130844 TCDEP1 Tropical Storm Fernanda Discussion Number 6 NWS National Hurricane Center Miami FL EP062017 300 AM MDT Thu Jul 13 2017 Fixes off of recent ASCAT data indicate that Fernanda's center is now fully embedded beneath the convective canopy, and cloud tops are as cold as -85 deg C. The improved structure is translating into stronger surface winds, with the ASCAT passes showing that the initial intensity is now 45 kt. The ASCAT data showed that Fernanda's center is moving south of due west, and the motion estimate is 265/9 kt. Deep-layer ridging to the north of the cyclone is expected to strengthen and build westward, which should keep Fernanda on a west to south-of-due-west trajectory for the next 3 days. The ridge then narrows and weakens a bit on days 4 and 5, which should allow Fernanda to gradually gain some latitude by the end of the forecast period. The recent trend of the track guidance shifting south has continued, and the updated NHC track forecast has therefore been shifted south of the previous forecast during the first 48 hours. After that time, the models are then suggesting that Fernanda's track may take a more pronounced poleward bend, and the new NHC forecast is therefore a little northeast of the previous forecast on days 4 and 5. Northeasterly shear affecting Fernanda has weakened as expected, and it's now analyzed to be about 10 kt. The shear is forecast to diminish further, and it should generally be below 10 kt for the remainder of the forecast period. In addition, Fernanda is currently moving over a warm pool where sea surface temperatures are about 29 deg C. This low-shear, high-SST environment should spark a significant intensification trend in the coming days. HCCA, the Florida State Superensemble (FSSE), and the COAMPS-TC model are all quite aggressive, showing Fernanda becoming a major hurricane just after 48 hours and continuing to strengthen through days 3 and 4. This scenario is supported by the SHIPS RI guidance, which gives a 50/50 chance of Fernanda reaching major hurricane strength in 48 hours. Based on these models, the NHC intensity forecast has been bumped upward, and it generally lies near a blend of HCCA, FSSE, and the ICON intensity consensus. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 11.7N 114.1W 45 KT 50 MPH 12H 13/1800Z 11.5N 115.5W 55 KT 65 MPH 24H 14/0600Z 11.2N 117.4W 65 KT 75 MPH 36H 14/1800Z 10.9N 119.3W 80 KT 90 MPH 48H 15/0600Z 10.9N 121.4W 95 KT 110 MPH 72H 16/0600Z 11.6N 125.9W 110 KT 125 MPH 96H 17/0600Z 12.8N 130.2W 115 KT 130 MPH 120H 18/0600Z 14.0N 134.0W 105 KT 120 MPH $$ Forecaster Berg
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