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Hurricane Rosa Forecast Discussion Number 11
2018-09-27 22:49:06| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Thu Sep 27 2018 742 WTPZ45 KNHC 272049 TCDEP5 Hurricane Rosa Discussion Number 11 NWS National Hurricane Center Miami FL EP202018 200 PM PDT Thu Sep 27 2018 Rosa is undergoing rapid intensification, accompanied by the formation of a well-defined 15 n mi wide eye inside the central dense overcast. Recent subjective and objective satellite intensity estimates are generally in the 100-115 kt range, and the initial intensity is increased to 110 kt in best agreement with the CIMSS ADT and the subjective Dvorak estimate from TAFB. Rosa continues to have good cirrus outflow in all directions. The intensity forecast has some complexities. The first is how much more Rosa will strengthen before the rapid intensification stops. The new intensity forecast follows the upper edge of the guidance in showing about 12 h more strengthening with a peak intensity of 120 kt. That being said, it would not be surprising if Rosa got stronger than that. The simplest part of the forecast is from 24-72 h, when the sea surface temperatures cool along the forecast track with Rosa gradually weakening as a result. After 72 h, the cyclone should move across the quite cold waters of the northeastern Pacific, and then move across Baja California over the warm water of the Gulf of California. While that is happening, a mid-latitude trough to the northwest is expected to cause both strong shear and strong upper-level divergence over Rosa. The intensity guidance responds to this combination of ingredients with intensity forecasts of anywhere between 30-65 kt as Rosa makes landfall on the Baja California peninsula. The new intensity forecast continues to call for Rosa to weaken to a tropical storm before reaching Baja California. However, this should be considered to be a low confidence forecast at this time. Rosa is farther south than estimated in the previous advisory, and the new initial motion is now 265/9. Other than that, there is no change in the forecast philosophy from the previous forecast. For the next 12 h or so, 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 the aforementioned 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 the northern Baja California peninsula and northwestern Mexico. The dynamical models show spread in both direction and speed as Rosa approaches Baja. The ECMWF and the Canadian models are on the left side of the envelope in forecasting landfall on the northern part of the peninsula, while the GFS and the HWRF are on the right side with a landfall closer to the central part of the peninsula. The new forecast track lies between those extremes near the center of the guidance envelope and the consensus models. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 16.9N 115.9W 110 KT 125 MPH 12H 28/0600Z 17.0N 117.0W 120 KT 140 MPH 24H 28/1800Z 17.5N 118.1W 120 KT 140 MPH 36H 29/0600Z 18.4N 118.7W 115 KT 130 MPH 48H 29/1800Z 19.8N 119.0W 105 KT 120 MPH 72H 30/1800Z 23.5N 119.0W 85 KT 100 MPH 96H 01/1800Z 26.5N 117.0W 60 KT 70 MPH 120H 02/1800Z 31.0N 114.0W 40 KT 45 MPH $$ Forecaster Beven
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