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Hurricane Fernanda Forecast Discussion Number 31
2017-07-19 16:40:46| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Wed Jul 19 2017 000 WTPZ41 KNHC 191440 TCDEP1 Hurricane Fernanda Discussion Number 31 NWS National Hurricane Center Miami FL EP062017 800 AM PDT Wed Jul 19 2017 While there are still occasional glimpses of the eye in infrared imagery, the convective cloud pattern of Fernanda continues to slowly decay. The initial intensity is thus reduced a little more, to 75 kt, based on a blend of various satellite intensity estimates. Water vapor imagery shows that the outflow is becoming restricted in the southwestern quadrant, which is a reflection of 10-15 kt of southwesterly vertical shear affecting the cyclone. The initial motion is 310/7. Fernanda is expected to turn west-northwest later today and continue this motion through 72 h as it is steered by a strong low- to mid-level ridge to the north. This ridge is forecast to persist after 72 h. However, the guidance becomes more divergent during that time, likely due to how quickly the various large-scale models weaken Fernanda. The NAVGEM and Canadian models, which weaken the cyclone quickly, show a generally westward motion of the remnants. The GFS and the HWRF, which maintain a stronger vortex, show a more northerly motion on the right side of the guidance envelope. The ECMWF is between these extremes, and this part of new track forecast is a little to the north of the ECMWF and a little south of the model consensus. Overall, the new forecast is little changed through 72 h, then nudged north of the previous forecast thereafter. Fernanda is expected to steadily weaken through the forecast period due to various combinations of cool sea surface temperatures, southwesterly to southerly shear, and dry air entrainment. Thus, the new forecast again follows the trend of the previous advisory and calls for Fernanda to weaken to a tropical storm in less than 24 h, a post-tropical low by 72 h, and a remnant low by 96 h. The new forecast is little changed from the previous forecast and lies close to the intensity consensus. It should be noted that the GFS and ECMWF show the possibility that Fernanda could interact with an upper-level trough north of the Hawaiian Islands in a way that could prolong its life as a tropical cyclone. Currently, the confidence in this happening is too low to justify a change to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 17.4N 135.5W 75 KT 85 MPH 12H 20/0000Z 17.9N 136.5W 65 KT 75 MPH 24H 20/1200Z 18.5N 138.0W 55 KT 65 MPH 36H 21/0000Z 19.0N 139.6W 45 KT 50 MPH 48H 21/1200Z 19.5N 141.3W 40 KT 45 MPH 72H 22/1200Z 20.5N 144.5W 35 KT 40 MPH...POST-TROPICAL 96H 23/1200Z 22.0N 149.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 24/1200Z 23.0N 153.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven
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