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Tropical Storm ROSLYN Forecast Discussion Number 6
2016-09-26 22:48:46| National Hurricane Center (East Pacific)
Issued at 200 PM PDT MON SEP 26 2016 000 WTPZ43 KNHC 262048 CCA TCDEP3 TROPICAL STORM ROSLYN DISCUSSION NUMBER 6...CORRECTED NWS NATIONAL HURRICANE CENTER MIAMI FL EP182016 200 PM PDT MON SEP 26 2016 CORRECTED STATUS AT 72H Although the center of Roslyn has become farther separated from the deep convection this afternoon due to strong southwesterly shear, recent ASCAT data indicate that the tropical cyclone is stronger than previously estimated. The 1756 UTC ASCAT overpass revealed 40-45 kt winds, and a much larger area of 34-kt winds than analyzed earlier. Based on these data, the initial intensity has been set at 45 kt, and the 34-kt wind radii have been expanded accordingly. Increasing southwesterly vertical wind shear and gradually decreasing SSTs should cause weakening, but given the large size of the system the spindown process is likely to be more gradual than average. In 24 to 36 hours, much cooler waters and a more stable airmass are expected to cause Roslyn to degenerate into a remnant low and to dissipate in 3 to 4 days. The NHC intensity forecast has been adjusted upward in the early portion of the forecast to account for the higher initial intensity, but is unchanged thereafter. The official forecast shows a slower rate of decay than the SHIPS guidance, but it is general agreement with the trend in the global models. Roslyn has not moved much during the past 24 hours, and the best estimate of the initial motion is 035/2 kt. The models insist that Roslyn will begin moving northeastward within deep layer southwesterly flow between a mid-level ridge to the southeast and a large upper-level low over Baja California. In a couple of days, the cyclone should turn northward, then northwestward once it weakens and is steered by the low-level flow. The new NHC track is similar to the previous advisory and is near a consensus of the ECMWF and GFS models. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 16.8N 118.8W 45 KT 50 MPH 12H 27/0600Z 17.3N 118.4W 40 KT 45 MPH 24H 27/1800Z 18.4N 117.7W 35 KT 40 MPH 36H 28/0600Z 19.8N 117.3W 30 KT 35 MPH 48H 28/1800Z 21.2N 117.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 29/1800Z 23.3N 118.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 30/1800Z...DISSIPATED $$ Forecaster Brown
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