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Tropical Storm Rosa Forecast Discussion Number 4
2018-09-26 04:39:50| National Hurricane Center (East Pacific)
Issued at 900 PM MDT Tue Sep 25 2018 649 WTPZ45 KNHC 260239 TCDEP5 Tropical Storm Rosa Discussion Number 4 NWS National Hurricane Center Miami FL EP202018 900 PM MDT Tue Sep 25 2018 Satellite imagery indicates that Rosa is still strengthening. The tropical storm has impressive banding features that wrap cyclonically from the northwest to northeast quadrant, though a dry slot has recently been observed infringing on the storm's developing inner-core. The most recent Dvorak intensity estimates from TAFB and SAB are 55 kt, so the initial intensity has been raised to that value. All of the intensity guidance suggests that rapid intensification (RI) is either already underway or imminent. SSMIS imagery from around 2300 UTC appeared to confirm the onset of RI with the development of a small low-level eye-like feature that has been associated with rapid intensification in past tropical cyclones. Although more recent imagery indicates this feature may have been disrupted by the aforementioned dry slot, the models suggest that this disruption may not last long. The NHC forecast therefore continues to show RI, and now calls for Rosa to become a major hurricane in about 36 h. Beyond that time, the hurricane is expected to remain in a fairly favorable environment through Friday, however, eyewall replacement cycles could limit the extent to which Rosa intensifies once it nears major hurricane strength. By the weekend, cooler SSTs and a drier surrounding environment should cause Rosa to begin weakening. The NHC intensity forecast is similar to the previous advisory, and is generally close to HCCA, especially beyond 48 h. Rosa is moving steadily west-northwestward, or 285/8 kt. A mid- level ridge to the north of Rosa should keep the cyclone on the same general heading for the next several days. There is still some large discrepancies between the global models on the strength of the ridge for the next few days, resulting in differences in the forward speed of Rosa during that time. By the end of the week, a large mid-latitude trough is expected to create a weakness in the ridge, allowing Rosa to turn northwestward, and possibly northward. The NHC track forecast will continue to follow the TVCE and HCCA consensus aids for this advisory. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 15.1N 109.7W 55 KT 65 MPH 12H 26/1200Z 15.5N 110.9W 70 KT 80 MPH 24H 27/0000Z 16.0N 112.5W 85 KT 100 MPH 36H 27/1200Z 16.3N 114.1W 100 KT 115 MPH 48H 28/0000Z 16.6N 115.8W 105 KT 120 MPH 72H 29/0000Z 17.8N 119.0W 110 KT 125 MPH 96H 30/0000Z 20.0N 120.4W 90 KT 105 MPH 120H 01/0000Z 22.0N 121.0W 75 KT 85 MPH $$ Forecaster Zelinsky
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