Highlight: Grace will be stronger than NOAA/NHC forecast due to very warm water surface. Southwest Gulf of Mexico major hurricane possible.
Fig. 1: Gulf of Mexico sea surface temperature analysis with annotated SST, NOAA/NHC forecast track of Grace and NOAA max windspeed forecast. Added is the max wind of tropical cyclone models forecast.
Discussion: Climate Impact Company upgrades the intensity risk forecast for Tropical Storm Grace to a potential category 3 major hurricane by later Friday in the southwest Gulf of Mexico. Right now, Grace is gaining organization as attendant thunderstorm activity is exploding around the core of this system. Once Grace is away from land (south of Cuba) strengthening to a hurricane should occur with ease. Sea surface temperatures (SST) are in the 85-86F range in the western Caribbean Sea (Fig. 1) which should provide enough upper ocean heat for Grace to reach a minimal category 2 hurricane prior to striking the Yucatan Peninsula Wednesday night. Some weakening occurs over the Yucatan Peninsula. However, 86-87F SST should fuel rapid intensification of Grace to a major hurricane once into the southwest Gulf of Mexico prior to making landfall early Saturday. The wind speed forecasts are the upper limit offered by tropical cyclone models (Fig. 2). A due west forecast track remains indicated. However, there are a couple of models indicating a northwesterly track (Fig. 3).
Fig. 2: Given the warm SST of the western Caribbean Sea and southwest Gulf of Mexico, the upper limit of tropical cyclone model windspeed forecasts for Grace is preferred.
Fig. 3: Tropical cyclone model tracks are mostly due west although 2 or 3 tracks are farther north with Grace.