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Tropical Storm RICK Forecast Discussion Number 8
2015-11-20 09:44:54| National Hurricane Center (East Pacific)
Issued at 200 AM MST FRI NOV 20 2015 000 WTPZ41 KNHC 200844 TCDEP1 TROPICAL STORM RICK DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212015 200 AM MST FRI NOV 20 2015 Rick is sending mixed signals tonight with regard to its organization and intensity. On one hand, the convective banding is a little better defined, and Dvorak T-numbers are now T3.0 from SAB and T2.5 from TAFB. On the other hand, recent scatterometer data indicate that the maximum winds remain about 35 kt, with the tropical-storm-force winds confined to a small area west of the center. The initial motion remains west-northwestward, or 295/11 kt. A mid-level ridge that extends westward across central Mexico is forecast to build farther westward over the Pacific waters during the next 24 hours, which should keep the cyclone on a west- northwestward course for the next couple of days. By Sunday, the western extent of the ridge will be eroded by a shortwave trough, causing Rick to turn gradually northwestward and northward on days 3-5. The track models all agree on this general scenario, but the overall guidance envelope has shifted westward from the previous cycle, especially beyond 36 hours. Therefore, the updated NHC track forecast is also shifted westward and lies very close to the TVCE model consensus and the Florida State Superensemble. Deep-layer shear near Rick is very low at the moment and should remain generally light for the next 36-48 hours. In addition, sea surface temperatures are sufficiently warm for intensification. However, a major limiting factor appears to be the presence of mid-level dry air, with the 700-500 mb relative humidity expected to remain around 50 percent for the next few days. Therefore, only slight strengthening is anticipated in the short term. After 48 hours, a marked increase in southwesterly shear should cause Rick to weaken and degenerate to a remnant low, possibly as early as 72 hours, when the associated deep convection is sheared away from the low-level center. The latest global models suggest that the remnant low may now last through 120 hours. There is not much spread among the intensity models, and the official intensity forecast mainly follows the IVCN model consensus. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 15.9N 109.4W 35 KT 40 MPH 12H 20/1800Z 16.5N 110.8W 40 KT 45 MPH 24H 21/0600Z 17.1N 112.4W 40 KT 45 MPH 36H 21/1800Z 17.6N 113.9W 40 KT 45 MPH 48H 22/0600Z 18.1N 115.1W 40 KT 45 MPH 72H 23/0600Z 20.1N 116.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 24/0600Z 22.0N 117.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 25/0600Z 22.5N 117.0W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg
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