The Tropical Disturbance 98L Report

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Discussion: Tropical Disturbance 98L is a ragged and disorganized area of low pressure located just north of the central northern coast of South America (Fig. 1). On either side of 98L, heavy thunderstorm activity is present. The area of low pressure is drifting westward just to the north of the coastline. Proximity to the coast is preventing organization. Ahead of 98L the shear pattern is ideal for tropical cyclone development in the central Caribbean Sea. NOAA/NHC indicates a 90% chance of a tropical storm in 48-72 hours.

Tropical cyclone models identify the most likely 5-6-day track…westward and then northwestward toward the southeast Gulf of Mexico (Fig. 2). Tropical cyclone model intensity forecasts are generally confident that this system will reach category-3 major hurricane strength in 120-132 hours in the northwest Caribbean Sea and the lead model (HWFI) indicating category-4 potential (Fig. 3).

Formation and strengthening of a tropical cyclone is certainly supported by the SST pattern in the Caribbean Sea. Widespread 85-86F is available, similar to SST where Fiona became a category-4 major hurricane (Fig. 4). The SSTA pattern is warmer than normal where 98L is forecast to track the next several days (Fig. 5).

In the Gulf of Mexico, surface water is plenty warm to support a major hurricane with widespread 85-86F available (Fig. 6). The northwest, north and northeast Gulf of Mexico are warmer than normal (Fig. 7).

Operational models have a different view of what the eventual hurricane/major hurricane will do tracking through the Gulf of Mexico. The ECM is consistent taking this storm into northern Florida next week (Fig. 8). However, GFS is slower (and stronger) and farther west with the hurricane/major hurricane offshore Louisiana in 10 days (Fig. 9). The GFS 11-15-day rainfall forecast indicates this system tracks northeastward through the Tennessee Valley to New England (Fig. 10).

In conclusion, the environment ahead for 98L is ideal for development and a tropical storm is likely by Saturday. Waters are very warm in the Caribbean Sea and steady intensification to a hurricane in 3-4 days and possibly a major hurricane while approaching the southeast Gulf of Mexico in 5-6 days is a reasonable expectation. Where this major hurricane tracks in the Gulf of Mexico is uncertain. GFS is stronger and farther west while ECM is fairly quick to turn this system northeastward into Florida. Keep in mind, GFS defeated ECM with the north (rather than northwest) track once north of Hispaniola with extended-range forecasts. The Gulf of Mexico is plenty warm to support a major hurricane.

Fig. 1: Western North Atlantic basin weather satellite view identifying Category-4 Major Hurricane Fiona and Tropical Disturbance 98L.

Fig. 2-3: Tropical cyclone models forecast tracks and intensity for Tropical Disturbance 98L.

Fig. 4-5: The Caribbean Sea SSTA and SSTA observations.


Fig. 6-7: The Gulf of Mexico SSTA and SSTA observations.

Fig. 8-10: The ECM and GFS 6-10-day rainfall forecasts (top) and GFS 11-15-day rainfall forecast (bottom).