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Tropical Depression TWENTY-ONE-E Forecast Discussion Number 2
2015-11-18 21:39:16| National Hurricane Center (East Pacific)
Issued at 200 PM MST WED NOV 18 2015 000 WTPZ41 KNHC 182039 TCDEP1 TROPICAL DEPRESSION TWENTY-ONE-E DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212015 200 PM MST WED NOV 18 2015 Overall, the cyclone's cloud pattern has changed little in organization since the previous advisory. The center of the depression is on the southeastern edge of a large cluster of deep convection, indicative of a continuation of moderate southeasterly shear. A well-defined swirl is also seen in visible satellite imagery, rotating around the south side of the estimated mean center. Satellite intensity estimates are a consensus T2.0 from TAFB and SAB, and the initial intensity estimate is held at 30 kt. The center has been moving erratically during the last 6 to 12 hours, with fixes during this time indicating a nearly stationary initial motion. The tail of a deep mid- to upper-level trough over the central United States extends southwestward to just north of the depression, which has created a weakness near 110W. The weakness has created a weak steering environment that should persist for about the next 12 to 24 hours and result in the depression's moving erratically or slowly northward around a weak mid-level high to the east. A turn toward the northwest and then west-northwest is expected after that time with an increase in forward speed when a mid-level anticyclone over the Gulf of Mexico builds westward into the eastern Pacific to the north of the cyclone. After that time, a trough currently between 130W and 140W in the subtropics is forecast to eject eastward toward the cyclone and result in a northward turn in 96 hours. The new track forecast is much faster than the previous forecast and adjusted to the left, especially beyond 48 hours, but is not as far west as the multi-model consensus. SHIPS model output indicates a lessening of southeasterly shear over the depression within 24 hours, with the shear remaining relatively low through about 72 hours. Meanwhile, the lower- to mid- tropospheric moisture is forecast to decrease some and be only marginally conducive for strengthening. However, since the cyclone should be over anomalously warm waters during this period, intensification is forecast, especially after the shear decreases. After 72 hours, a tremendous increase in southwesterly shear ahead of the trough advancing from the west should result in rapid weakening, with remnant low status likely in 96 to 120 hours. The new intensity forecast is a bit higher than the previous one in agreement with the latest SHIPS/LGEM guidance and remains slightly above the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 12.8N 107.0W 30 KT 35 MPH 12H 19/0600Z 13.4N 107.2W 35 KT 40 MPH 24H 19/1800Z 14.3N 108.4W 40 KT 45 MPH 36H 20/0600Z 15.2N 110.1W 50 KT 60 MPH 48H 20/1800Z 15.6N 111.5W 55 KT 65 MPH 72H 21/1800Z 17.2N 114.5W 60 KT 70 MPH 96H 22/1800Z 18.6N 115.8W 30 KT 35 MPH 120H 23/1800Z 20.5N 116.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Kimberlain
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