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Tropical Depression Eighteen-E Forecast Discussion Number 1
2020-09-29 10:43:25| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Tue Sep 29 2020 000 WTPZ43 KNHC 290843 TCDEP3 Tropical Depression Eighteen-E Discussion Number 1 NWS National Hurricane Center Miami FL EP182020 300 AM MDT Tue Sep 29 2020 A burst of deep convection that developed near the center of the area of low pressure well southwest of the southwestern coast of Mexico during the evening has persisted overnight. Microwave imagery and a 0444 UTC ASCAT-C overpass indicated that the center of the low re-formed within the area of deep convection and with the overall increase in the organization of the system, advisories are being initiated on the eighteen tropical depression of the 2020 eastern Pacific hurricane season. The scatterometer data revealed peak winds of around 30 kt, and that is used as the advisory intensity. The depression is located over warm water and within an area of light to moderate northeasterly shear, and these conditions are expected to allow for steady strengthening over the next few days. Although the SHIPS model guidance only shows a peak intensity of 65-70 kt in 72-84 hours, the SHIPS rapid intensification index indicates a 50 percent chance of a 65 kt increase in intensity over the next 72 hours. In addition, the global models significantly deepen the system over the next few days. On the basis of the SHIP RI information and the global models, the NHC intensity forecast is above the IVCN intensity consensus close to the more aggressive HWRF and HCCA models. Late in the period, decreasing SSTs and increasing vertical wind shear should result in weakening. Given the recent re-formation of the center, the initial motion estimate is a highly uncertain 275/9 kt. A deep-layer ridge centered over the southwestern United States is expected to steer the cyclone westward to west-northwestward during the next several days. By the end of the forecast period, the cyclone will be approaching the southwestern portion of the ridge allowing it to turn northwesterly. Although there some model differences in the predicted forward speed of the depression, the models are in good agreement on the overall track forecast scenario. To account for these forward speed differences, the NHC forecast is near the middle of the guidance envelope close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 13.2N 107.6W 30 KT 35 MPH 12H 29/1800Z 13.5N 109.0W 35 KT 40 MPH 24H 30/0600Z 14.2N 111.2W 45 KT 50 MPH 36H 30/1800Z 14.6N 114.3W 55 KT 65 MPH 48H 01/0600Z 14.8N 117.3W 65 KT 75 MPH 60H 01/1800Z 15.3N 119.9W 75 KT 85 MPH 72H 02/0600Z 16.2N 122.3W 85 KT 100 MPH 96H 03/0600Z 18.3N 126.2W 80 KT 90 MPH 120H 04/0600Z 20.5N 129.2W 60 KT 70 MPH $$ Forecaster Brown
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