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Tropical Storm Rosa Forecast Discussion Number 5
2018-09-26 10:45:25| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Wed Sep 26 2018 934 WTPZ45 KNHC 260845 TCDEP5 Tropical Storm Rosa Discussion Number 5 NWS National Hurricane Center Miami FL EP202018 300 AM MDT Wed Sep 26 2018 After steadily intensifying yesterday, Rosa's strengthening trend has temporarily paused. The tropical storm has a well-defined curved band that wraps about three-quarters of the way around the center. However, some dry air appears to be intruding into the core from the northeastern quadrant, which could be the reason why Rosa has stopped strengthening for now. The Dvorak classifications from TAFB and SAB remain 3.5/55 kt, so the initial intensity is held at that value. This wind speed is also close to the latest SATCON estimate from CIMSS at the University of Wisconsin. A strengthening trend is expected to resume soon, and it seems likely that Rosa will rapidly intensify during the next couple of days while it remains over warm SSTs and in an environment of low wind shear of 10 kt or less. The NHC intensity forecast closely follows the HCCA model, and brings Rosa to hurricane strength later today and major hurricane strength on Thursday. Beyond a few days, steady weakening is forecast due to cooler SSTs, dry and stable air, and an increase in southwesterly wind shear. The tropical storm is moving west-northwestward at 7 kt, steered by a mid-level ridge to its north. A west to west-northwest motion at about the same forward speed is expected for the next couple of days as the pattern holds. After that time, the ridge is expected to break down as a large, deep-layer low moves toward the U.S. west coast. This change in the steering flow should cause Rosa to move northwestward late Friday and Saturday and then northward late in the weekend. The models have come into a little better agreement this cycle, and a slight eastward shift has been made at 96- and 120-hours based on this guidance. This forecast lies fairly close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 15.5N 110.4W 55 KT 65 MPH 12H 26/1800Z 15.9N 111.5W 70 KT 80 MPH 24H 27/0600Z 16.2N 113.2W 85 KT 100 MPH 36H 27/1800Z 16.5N 115.0W 100 KT 115 MPH 48H 28/0600Z 16.8N 116.7W 105 KT 120 MPH 72H 29/0600Z 18.3N 119.0W 105 KT 120 MPH 96H 30/0600Z 20.7N 120.3W 85 KT 100 MPH 120H 01/0600Z 23.0N 120.0W 65 KT 75 MPH $$ Forecaster Cangialosi
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