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Tropical Storm John Forecast Discussion Number 4
2018-08-06 17:23:27| National Hurricane Center (East Pacific)
Issued at 900 AM MDT Mon Aug 06 2018 669 WTPZ42 KNHC 061522 CCB TCDEP2 Tropical Storm John Discussion Number 4...Corrected NWS National Hurricane Center Miami FL EP122018 900 AM MDT Mon Aug 06 2018 Corrected to remove the percent symbols in the text Early morning visible satellite images and recent microwave data show that John continues to quickly become better organized. Banding features now wrap nearly completely around the center, with the development of a fairly symmetric CDO. One-minute GOES-16 imagery also show several overshooting convective cloud tops near and to the east of the center. A TAFB Dvorak estimate of T3.5 was the basis of the 1200 UTC intensity of 55 kt, but with the increase in organization since that time, and raw objective T-numbers above 4.0 for the past few hours, the advisory intensity has been increased to 60 kt. John is within a very favorable environment for intensification. The hurricane will be moving over SSTs around 30C, and in a low shear and moist environment. These conditions are expected to allow for rapid strengthening during the next day or so. The SHIPS Rapid Intensification Index shows a nearly 80 percent chance of RI over the the next 24 h, and DTOPS gives an 80 percent chance of a 40 kt increase in intensity during the next 24 h. Based on these data and the very aggressive guidance, the NHC forecast calls for a 40 kt increase in strength from 1200 this morning through 1200 UTC Tuesday. The NHC forecast calls for a peak intensity that is close to the FSSE and HCCA models in 36 to 48 hours. After that time, John will be moving over cooler waters and into a more stable environment which is expected to cause rapid weakening. John is moving west-northwestward at about 7 kt. The tropical storm should turn northwestward and accelerate over the next day or so as it is steered around the western portion of a mid-level ridge that is centered over northern Mexico. As noted in the previous discussion, some interaction with Ileana is likely, which could cause some slow down of the forward speed of John. However since John is the larger system, it should remain the dominant tropical cyclone. The latest dynamical model guidance was similar to the previous cycle and no significant change to the NHC forecast was required. The NHC forecast is in best agreement with the ECMWF and is close to the HFIP corrected consensus. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 15.5N 107.9W 60 KT 70 MPH 12H 07/0000Z 16.0N 108.6W 75 KT 85 MPH 24H 07/1200Z 17.0N 109.6W 95 KT 110 MPH 36H 08/0000Z 18.3N 111.0W 110 KT 125 MPH 48H 08/1200Z 19.8N 112.7W 110 KT 125 MPH 72H 09/1200Z 22.9N 116.6W 85 KT 100 MPH 96H 10/1200Z 25.5N 120.7W 55 KT 65 MPH 120H 11/1200Z 26.8N 125.0W 35 KT 40 MPH...POST-TROPICAL $$ Forecaster Brown
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