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Tropical Storm ORLENE Forecast Discussion Number 2
2016-09-11 10:37:02| National Hurricane Center (East Pacific)
Issued at 200 AM PDT SUN SEP 11 2016 000 WTPZ41 KNHC 110836 TCDEP1 TROPICAL STORM ORLENE DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL EP162016 200 AM PDT SUN SEP 11 2016 There has been an impressive increase in the organization of the depression's cloud pattern since the last advisory. An ASCAT pass indicates that the low-level center is located just inside what appears to be a formative central dense overcast (CDO), whose cloud top temperatures have cooled significantly. A well-developed convective band also spirals outward from the CDO, now covering much of the western semicircle of the circulation. The earlier ASCAT pass showed peak uncontaminated winds of 32 kt. Given this datum, a satellite classification of T2.5 from TAFB, and some further increase in organization since the time of the pass, the initial intensity estimate is increased to 35 kt. The best estimate of Orlene's initial motion estimate is 315/11. The cyclone should move west-northwestward to northwestward around the southwestern periphery of a mid-level ridge over northern Mexico today. In 24 to 48 hours, Orlene's forward motion should decrease significantly when the cyclone encounters a weakness in the subtropical ridge between 120W and 125W, caused by a southward extension of a mid- to upper-level trough near the United States West Coast. A further reduction in forward speed and a turn toward the north-northwest is expected by 72 hours, and Orlene could even come to a halt in the face of weak steering around this time. There is widespread agreement in the guidance that the subtropical ridge will re-establish itself north of Orlene in about 4 days, which should result in a westward or possibly a west-southwestward motion with an increase in forward speed. Overall, little change was made to the previous forecast track, and the current one is close to a consensus based on the ECMWF and GFS solutions. East-northeasterly shear currently over Orlene is forecast to diminish during the next couple of days while the cyclone moves over warm waters. Steady strengthening is expected, even though the mid-level moisture will be only marginally favorable and SSTs will begin to gradually lower. If Orlene can quickly establish an inner core, the result could be greater intensification than this forecast predicts. The intensity forecast becomes challenging after 48 hours since Orlene should be straddling the 26.5-deg C isotherm for the remainder of the forecast period while the environmental moisture becomes critically low. There could also be some temporary increase in southwesterly shear. The combination of these factors should result in a steady-state or slowly weakening cyclone from 72-120 hours. The NHC intensity forecast is a little above the previous one, near the multi-model consensus, but lower than the SHIPS and FSU Superensemble output. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 14.8N 115.9W 35 KT 40 MPH 12H 11/1800Z 15.8N 117.4W 45 KT 50 MPH 24H 12/0600Z 16.8N 119.0W 55 KT 65 MPH 36H 12/1800Z 17.6N 120.0W 65 KT 75 MPH 48H 13/0600Z 18.2N 120.5W 75 KT 85 MPH 72H 14/0600Z 19.1N 120.9W 75 KT 85 MPH 96H 15/0600Z 19.1N 123.1W 70 KT 80 MPH 120H 16/0600Z 18.8N 127.2W 65 KT 75 MPH $$ Forecaster Kimberlain
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