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Tropical Depression EIGHT-E Forecast Discussion Number 1
2016-07-21 22:37:41| National Hurricane Center (East Pacific)
Issued at 300 PM MDT THU JUL 21 2016 000 WTPZ43 KNHC 212037 TCDEP3 TROPICAL DEPRESSION EIGHT-E DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP082016 300 PM MDT THU JUL 21 2016 An ASCAT-B pass at 1742Z showed that the area of low pressure located well southwest of Mexico now has a well-defined center, and the geostationary imagery shows a curved convective band wrapping nearly halfway around the system. Given this, the low is now classified as a tropical cyclone. The initial intensity is set to 30 kt based on the ASCAT data, which is also in agreement with the latest Dvorak estimate from SAB. The depression will be moving over SSTs of 28C or higher for the next couple of days, but will also be in a moderate easterly to northeasterly shear environment during that time. Given these conditions, gradual intensification is forecast in the short term. The cyclone is forecast to peak in about 72 hours before it moves over cooler waters and into a more stable environment, which should result in slow weakening. The NHC intensity prediction is close to the intensity consensus through the forecast period. The initial motion estimate is a somewhat uncertain 290/10 given the recent formation of the system. The dominant steering mechanism for the first 2-3 days of the forecast period will be a large subtropical ridge that will migrate westward from central North America over the eastern Pacific. This should keep the cyclone moving generally west-northwestward for the first 48 hours or so. After that time, there is an increase in the spread of the guidance. The ECMWF and HWRF show the cyclone turning more poleward into a weakness in the ridge caused by an upper-level low, with the ECMWF showing some northward motion possibly due to the influence of Tropical Storm Fred to the the northeast. The GFS, GEFS mean, and COAMPS-TC show a more westward track with the cyclone staying south of the ridge. For now the NHC track forecast is down the middle of the guidance envelope and is very close to the multi-model consensus. Given the large spread in the guidance, the track forecast uncertainty is higher than usual late in the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 21/2100Z 10.8N 114.0W 30 KT 35 MPH 12H 22/0600Z 11.4N 115.5W 35 KT 40 MPH 24H 22/1800Z 12.3N 117.6W 45 KT 50 MPH 36H 23/0600Z 13.0N 119.9W 50 KT 60 MPH 48H 23/1800Z 13.6N 122.0W 60 KT 70 MPH 72H 24/1800Z 15.0N 125.0W 65 KT 75 MPH 96H 25/1800Z 17.0N 128.0W 55 KT 65 MPH 120H 26/1800Z 18.0N 130.0W 50 KT 60 MPH $$ Forecaster Brennan
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