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Tropical Storm Sergio Forecast Discussion Number 7
2018-10-01 04:37:05| National Hurricane Center (East Pacific)
Issued at 900 PM MDT Sun Sep 30 2018 903 WTPZ41 KNHC 010237 TCDEP1 Tropical Storm Sergio Discussion Number 7 NWS National Hurricane Center Miami FL EP212018 900 PM MDT Sun Sep 30 2018 Overall, Sergio has changed little in organization over the past several hours. The convective pattern is comprised of a ragged band wrapping about three-quarters of the way around the center, with the strongest convection to the north of the center. Recent microwave data show that the mid-level circulation center seen earlier has lost some definition. However, the low-level circulation center seems to be becoming better defined. The initial intensity remains 55 kt based on unchanged satellite intensity estimates. The initial motion remains 260/11. For the next 36 h or so, Sergio should move westward or just south of due westward around the southern periphery of a large deep-layer subtropical ridge extending from Mexico westward across the eastern Pacific. After that time, a mid- to upper-level trough moving southeastward along and offshore of the western U.S. will erode the western part of the ridge. This development will allow Sergio turn west-northwestward to northwestward with a gradual decrease in forward speed. The new forecast track is near the various consensus models and is an update of the previous track. Conditions appear favorable for Sergio to rapidly intensify in the next 36 h if the cyclone can become well enough organized to take advantage of the environment. This part of the intensity forecast presumes this will happen and is unchanged from the previous forecast of quick strengthening. From 36-48 h, a burst of northeasterly shear is expected to affect Sergio, which should at least slow intensification. Based on this and the shear letting up at 72 h, the intensity forecast is tweaked to show the peak intensity after the shear decreases. After 72 h, decreasing sea surface temperatures along the forecast track should cause a gradual weakening. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 11.6N 107.3W 55 KT 65 MPH 12H 01/1200Z 11.4N 109.0W 65 KT 75 MPH 24H 02/0000Z 11.3N 111.3W 80 KT 90 MPH 36H 02/1200Z 11.6N 113.4W 95 KT 110 MPH 48H 03/0000Z 12.4N 115.2W 100 KT 115 MPH 72H 04/0000Z 14.5N 118.0W 105 KT 120 MPH 96H 05/0000Z 16.5N 120.5W 100 KT 115 MPH 120H 06/0000Z 18.0N 122.5W 90 KT 105 MPH $$ Forecaster Beven
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