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Tropical Depression TWENTY-ONE-E Forecast Discussion Number 1
2015-11-18 16:57:12| National Hurricane Center (East Pacific)
Issued at 1000 AM MDT WED NOV 18 2015 000 WTPZ41 KNHC 181557 TCDEP1 TROPICAL DEPRESSION TWENTY-ONE-E SPECIAL DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212015 1000 AM MDT WED NOV 18 2015 The circulation associated with the low pressure system located several hundred miles south-southeast of the southern tip of Baja California has become well-defined overnight according to scatterometer data. These data and first-light visible satellite imagery also indicate the that center of the cyclone is near the southeastern edge of large mass of cold-topped convection, suggesting the presence of some southeasterly shear. A Dvorak classification of T2.0 from TAFB, along with the earlier scatterometer data, is used to set the intensity to 30 kt. Since the history of fixes on this system is short, the initial motion estimate of 360/02 is somewhat uncertain. A deep trough over the central United States has created a significant weakness along 110W, which has made for a weak steering environment around the depression. However, a weak mid-level anticyclone to the south of mainland Mexico has been imparting a slow northward motion. This motion should continue for another 24 hours, at which time a mid-level ridge over the Gulf of Mexico is forecast to build westward into the eastern Pacific when the central U.S. trough lifts out. The building ridge should result in a northwestward and then a west-northwestward track through 72 hours. After that time, a trough currently between 130W and 140W in the subtropics is forecast to eject eastward toward the cyclone and result in its recurvature in about 96 hours. The official forecast track is on the left side of the guidance envelope, closest to the ECMWF and GFS solutions, and generally near the multi-model consensus. There are mixed signals on the potential for intensification in the short term. Although the waters are anomalously warm, some southeasterly shear is likely to continue to affect the cyclone over the next day or two, along with some drying of the lower to middle troposphere. These large-scale conditions suggest that some strengthening should occur, but it likely would be tempered by these two negative factors. Around 72 hours, the cyclone should encounter an environment of increasing south-southwesterly or southwesterly shear associated with the trough advancing from the west and rapidly weaken, likely becoming a remnant low by day 5, if not sooner. The official intensity forecast is a little above the multi-model consensus and closest to the ECMWF SHIPS output. FORECAST POSITIONS AND MAX WINDS INIT 18/1600Z 13.0N 107.2W 30 KT 35 MPH 12H 19/0000Z 13.3N 107.2W 35 KT 40 MPH 24H 19/1200Z 13.8N 107.5W 40 KT 45 MPH 36H 20/0000Z 14.8N 108.6W 45 KT 50 MPH 48H 20/1200Z 15.8N 110.6W 50 KT 60 MPH 72H 21/1200Z 16.4N 113.0W 45 KT 50 MPH 96H 22/1200Z 18.1N 114.2W 30 KT 35 MPH 120H 23/1200Z 20.5N 114.4W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Kimberlain
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