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Tropical Storm RICK Forecast Discussion Number 7
2015-11-20 03:40:21| National Hurricane Center (East Pacific)
Issued at 800 PM MST THU NOV 19 2015 000 WTPZ41 KNHC 200240 TCDEP1 TROPICAL STORM RICK DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212015 800 PM MST THU NOV 19 2015 Rick's cloud pattern has eroded some during the past 6 hours with previously solid bands of convection in the northern semicircle having become more fragmented during the past few hours. In addition, numerous small arc cloud lines have been noted propagating away from the cyclone, which is indicative of dry mid-level air having penetrated into the inner core region. This supposition is further supported by a 20/0006 UTC AMSU pass indicating only a narrow fragmented band of convection is present in the northwestern quadrant of the storm. Therefore, the initial intensity of 35 kt remains unchanged for this advisory, which is lower than the available satellite intensity estimates. The initial motion estimate is 295/09 kt and is based primarily on passive microwave satellite data. A mid-level ridge over central Mexico is forecast to build westward to the north and east of Rick during the next 24-36 hours, while a large upper-level low located near 27N 138W is expected to fill and gradually open up into a broad trough by 48-72 hours. The combination of these two steering mechanisms should keep Rick moving west-northwestward for the next 48 hours, followed by a decrease in forward speed and a gradual turn toward the northwest and north at 72 h and 96 h, respectively. The official forecast track was only nudged slightly to the left of the previous advisory track, and essentially lies down the middle of NHC track guidance envelope. Rick is forecast to move into a weak vertical wind shear regime during the next 24-36 hours while remaining over SSTs of 29 deg C. These favorable conditions would normally support intensification of a tropical cyclone. However, the ragged and elongated inner-core wind field, coupled with additional entrainment of drier mid-level air, is expected to inhibit any significant development and organization of deep convection. By 48 hours and beyond, an increase in southwesterly vertical wind shear to more than 25 kt is forecast to induce gradual weakening, with Rick becoming a remnant low by 96 hours when the cyclone will be moving over cooler waters at that time. Rick is expected to dissipate day 5, if not sooner. NHC intensity forecast is a little lower than the previous advisory and remains below the multi-model consensus, IVCN. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 15.2N 108.1W 35 KT 40 MPH 12H 20/1200Z 15.9N 109.5W 40 KT 45 MPH 24H 21/0000Z 16.5N 111.1W 40 KT 45 MPH 36H 21/1200Z 17.2N 112.4W 40 KT 45 MPH 48H 22/0000Z 17.8N 113.4W 35 KT 40 MPH 72H 23/0000Z 19.5N 115.0W 25 KT 30 MPH 96H 24/0000Z 21.6N 115.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 25/0000Z...DISSIPATED $$ Forecaster Stewart
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