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Hurricane Rosa Forecast Discussion Number 10
2018-09-27 16:54:05| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Thu Sep 27 2018 697 WTPZ45 KNHC 271454 TCDEP5 Hurricane Rosa Discussion Number 10 NWS National Hurricane Center Miami FL EP202018 800 AM PDT Thu Sep 27 2018 Rosa is becoming better organized. Conventional satellite imagery show a large area of cold cloud tops near the center, and there is a hint of an eye in the first-light visible images. Microwave imagery indicates that the eye structure underneath the overcast has become better defined, with less evidence of dry air entrainment than seen yesterday. The initial intensity has been increased to 90 kt in best agreement with the subjective Dvorak estimate from TAFB and the CIMSS ADT technique. The hurricane currently has good outflow in all directions. Conditions appear generally favorable for continued strengthening for the next 24-36 hr, and the new intensity forecast now makes Rosa a major hurricane in 12 h. It should be noted that if the current strengthening is the start of the previously anticipated rapid intensification Rosa could get stronger than the current forecast, which shows a peak intensity of 105 kt near the upper edge of the intensity guidance. After 36 h, the forecast track takes the cyclone over decreasing sea surface temperatures, and by the end of the forecast period it is expected to encounter strong southwesterly vertical shear. This combination should cause significant weakening, and Rosa is expected to be a tropical storm as it approaches the Baja California peninsula near the end of the forecast period. The initial motion is a somewhat uncertain 270/10. For the next 12-24 h, the hurricane should move generally westward on the south side of the subtropical ridge over the Pacific west of northern Mexico and a mid-latitude ridge over California. Subsequently, Rosa should turn northwestward and northward through a break in the ridge caused by a large mid-latitude trough moving eastward through the northeastern Pacific. By 96-120 h, Rosa should recurve northeastward into the westerlies on the eastern side of the trough and move in the general direction of northwestern Mexico and the northern Baja California peninsula. There remains some spread in the guidance forward speed after recurvature, with the GFS being faster than the ECMWF. The new intensity forecast is a blend of these extremes in forward speed at the 96 and 120 h points. Overall, the guidance envelope has shifted a little west since the previous advisory, and the new track is also shifted a little westward. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 17.2N 115.4W 90 KT 105 MPH 12H 28/0000Z 17.3N 116.9W 100 KT 115 MPH 24H 28/1200Z 17.5N 118.1W 105 KT 120 MPH 36H 29/0000Z 18.3N 119.0W 105 KT 120 MPH 48H 29/1200Z 19.5N 119.4W 100 KT 115 MPH 72H 30/1200Z 22.5N 119.5W 80 KT 90 MPH 96H 01/1200Z 26.0N 118.0W 60 KT 70 MPH 120H 02/1200Z 29.5N 115.5W 40 KT 45 MPH $$ Forecaster Beven
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