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Hurricane Grace Forecast Discussion Number 30
2021-08-20 22:45:15| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Fri Aug 20 2021 000 WTNT42 KNHC 202045 TCDAT2 Hurricane Grace Discussion Number 30 NWS National Hurricane Center Miami FL AL072021 400 PM CDT Fri Aug 20 2021 The satellite presentation of Grace has greatly improved over the past several hours. Deep convection has become more concentrated over the center, and the central dense overcast now appears more symmetric. Dropsonde winds and peak 850-mb flight level wind measured by the Air Force Hurricane Hunters around midday were consistent with an intensity of around 75 kt. However, the surface pressure has been gradually falling throughout the day, and recent satellite data suggest the hurricane is becoming better organized. Therefore, the initial intensity is raised to 80 kt for this advisory, which is supported by the latest UW-CIMSS objective ADT estimate. Given the high oceanic heat content within the southwestern Gulf of Mexico, additional strengthening is expected through Grace's landfall tonight. The 10-15 kt of northerly vertical wind shear over Grace does not appear to be having much of a negative effect on the cyclone at this time. Thus, the official NHC intensity forecast remains on the high end of the guidance envelope, and is closest to the statistical-dynamical models DSHP and LGEM. The current forecast shows Grace making landfall within the next 12-18 h. Once the center of Grace moves inland over the mountains of central Mexico, the cyclone should rapidly weaken and then dissipate by 48 h. However, its remnants appear likely to move into the eastern Pacific and lead to the development of a new tropical cyclone in that basin later this weekend or early next week. Earlier reconnaissance data indicate that Grace has slowed down a bit today, and its initial motion is estimated to be 265/9 kt. This general motion should continue through landfall as Grace is steered by a mid-level ridge over the northern Gulf of Mexico. The official NHC track forecast is slightly slower, but otherwise very similar to the previous one and lies near the center of the guidance envelope. Key Messages: 1. Hurricane conditions and dangerous storm surge are likely along portions of the coast of eastern mainland Mexico beginning this evening within the Hurricane Warning area from Puerto Veracruz northward to Cabo Rojo. 2. Through the weekend, heavy rainfall across Veracruz, Puebla, Tlaxcala, Hidalgo, northern Queretaro, and eastern San Luis Potosi will lead to significant flash and urban flooding, along with the likelihood of mudslides. FORECAST POSITIONS AND MAX WINDS INIT 20/2100Z 20.5N 95.1W 80 KT 90 MPH 12H 21/0600Z 20.4N 96.6W 90 KT 105 MPH...NEAR THE COAST 24H 21/1800Z 19.9N 98.9W 45 KT 50 MPH...INLAND 36H 22/0600Z 19.5N 101.9W 30 KT 35 MPH...INLAND 48H 22/1800Z...DISSIPATED $$ Forecaster Reinhart/Cangialosi
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