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Tropical Storm Rene Forecast Discussion Number 12
2020-09-10 04:34:35| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Wed Sep 09 2020 000 WTNT43 KNHC 100234 TCDAT3 Tropical Storm Rene Discussion Number 12 NWS National Hurricane Center Miami FL AL182020 1100 PM AST Wed Sep 09 2020 Rene remains a sheared tropical cyclone, with modest mid-/upper-level easterly vertical wind shear of 12-15 kt undercutting the otherwise favorable outflow layer. The combination of the shear and intrusions of dry mid-level air have caused the convective pattern to continue to fluctuate since the previous advisory. Although a recent burst of deep convection has again pulsed near and to he west of the center, the intensity is being maintained at 35 kt based on a 09/2305Z ASCAT-A overpass indicating barely 34 kt winds in the northwest quadrant. The 34-kt wind radius was also expanded in that quadrant based on the ASCAT wind data. The initial motion remains west-northwestward motion or 285/11 kt. Under the influence of a mid-level ridge, Rene is expected to continue moving west-northward over the eastern Atlantic for the next few days. A weakness in the ridge is forecast to develop around 40W-45W longitude, which will be partly induced by Tropical Storm Paulette's circulation, causing Rene to slow down and turn toward the northwest and then north-northwest on 3-4 days. By day 5, Rene's northward motion is forecast to be blocked significantly by a building ridge to the north of the cyclone as TS Paulette moves farther away. It is possible that Rene could stall or even make a small looping motion if the storm gets trapped within the much larger ridge. The new NHC forecast is to the left or south of the previous advisory track, but not as far left as the consensus models or the preponderance of the remaining guidance. Rene's upper-level outflow is forecast to remain intact for the next 60 h or so, which would should allow for at least gradual strengthening during that time. The shear is forecast by both the GFS and the ECMWF models to decrease to near zero in the 36-48 h time frame, and that is when Rene should be able to take advantage of marginal sea-surface temperatures (SST) of 26.5C and modest mid-level humidity conditions, and obtain hurricane status in 48-60 h. Thereafter, strong west-northwesterly shear is expected to induce gradual weakening despite the cyclone moving over warmer SSTs of 27-28C. The official intensity forecast is similar to the GFS model intensity forecast, and lies below the simple consensus model IVCN and the corrected-consensus models HCCA and FSSE. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 18.0N 34.0W 35 KT 40 MPH 12H 10/1200Z 18.4N 35.5W 40 KT 45 MPH 24H 11/0000Z 18.9N 37.4W 45 KT 50 MPH 36H 11/1200Z 19.4N 39.3W 50 KT 60 MPH 48H 12/0000Z 20.5N 41.4W 60 KT 70 MPH 60H 12/1200Z 21.8N 43.2W 65 KT 75 MPH 72H 13/0000Z 23.5N 45.1W 60 KT 70 MPH 96H 14/0000Z 26.8N 46.5W 50 KT 60 MPH 120H 15/0000Z 28.3N 47.6W 40 KT 45 MPH $$ Forecaster Stewart
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