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Tropical Storm Marie Forecast Discussion Number 5
2020-09-30 10:37:34| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Wed Sep 30 2020 000 WTPZ43 KNHC 300837 TCDEP3 Tropical Storm Marie Discussion Number 5 NWS National Hurricane Center Miami FL EP182020 300 AM MDT Wed Sep 30 2020 Geostationary satellite imagery shows that Marie continues to become better organized with a curved band of convection over the western semicircle and a small central dense overcast feature. An ASCAT-B overpass from around 0515 UTC was very helpful in pinpointing the center, and it also revealed that Marie's tropical-storm-force wind field is quite small. Subjective satellite intensity estimates of T3.0 and the scatterometer data yielded an intensity of 45 kt at 0600 UTC, but given the continued improvement in organization, the advisory intensity has been set at 50 kt. Although Marie's outflow is somewhat restricted over the northeastern portion of the storm due to some northeasterly shear, it has been expanding over the past few hours indicating that the shear is decreasing as anticipated. Marie is forecast to remain over warm waters and in a low shear environment during the next couple of days. These very conducive conditions favor strengthening, and the NHC intensity forecast calls for steady to rapid intensification over the next 48 hours. The official forecast is in good agreement with the SHIPS, LGEM, and HFIP corrected consensus models which all predict periods of rapid strengthening over the next 48 to 60 hours. The updated NHC wind speed forecast shows a faster rate of strengthening and a slightly higher peak intensity than in the previous advisory. After 72 hours, cooler waters and a more stable environment should result in steady to rapid weakening. Maria is moving westward at about 14 kt, a little faster than before. There has been no change to the track forecast philosophy as Marie is expected to move westward to west-northwestward during the next few days while it remains to the south of a deep-layer ridge. After that time, a slower northwestward motion is predicted when Marie approaches a weakness in the ridge. The latest runs of the dynamical models have trended toward a more westward track during the first 60 hours or so, and the official forecast has been adjusted accordingly. Thereafter, the NHC track is fairly similar to the previous advisory, and it again lies near the middle of the guidance envelope. Marie's 12-ft sea radii remain larger than would be expected for a small tropical storm due to a large fetch of southerly swell originating from the Southern Hemisphere. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 14.1N 112.5W 50 KT 60 MPH 12H 30/1800Z 14.4N 114.8W 60 KT 70 MPH 24H 01/0600Z 14.5N 117.7W 75 KT 85 MPH 36H 01/1800Z 14.9N 120.5W 90 KT 105 MPH 48H 02/0600Z 15.7N 123.1W 105 KT 120 MPH 60H 02/1800Z 16.8N 125.3W 110 KT 125 MPH 72H 03/0600Z 18.0N 127.2W 100 KT 115 MPH 96H 04/0600Z 20.0N 130.2W 75 KT 85 MPH 120H 05/0600Z 21.5N 133.0W 55 KT 65 MPH $$ Forecaster Brown
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