WeatherTiger's Invest 99L Forecast Update for November 13th

A Caribbean disturbance may menace Florida next week, but there is uncertainty in what form this system could take.

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Florida and continental U.S. tropical threat synopsis: A Caribbean tropical disturbance, Invest 99L, remains a possible hurricane threat to Florida in about a week and should continue to be monitored closely.

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Do we really have to go through all of this again?

This question is on the minds of millions of Floridians as hurricane season again displays the tenacity of the cockroach and prepares to disgorge another Gulf Coast threat. While an eventual Florida impact is a possible scenario, any potential landfall remains around 7 days out, and there is still much uncertainty as to what actually moves into the Gulf next week.

If you feel that you should not have to be dealing with this, I strongly share your sentiment. Of the 642 tropical storm or hurricane landfalls on record in the continental U.S. since the 1850s, only 4 occurred after November 15, and just one, 1985’s Kate, was a hurricane. All four struck the Florida Gulf Coast.

Month-to-date average temperature deviations from normal for November 2024. (PRISM/Oregon State U.)

However, November hurricane history really isn’t the right frame of reference, as weather patterns over the past three weeks have more in common with typical conditions in late September or early October. Temperatures to start off the month are averaging 5 degrees above normal in Miami, 10 degrees above normal in Tampa, and a whopping 15 degrees above normal in Tallahassee and elsewhere across the Deep South, coupled with minimal rainfall.

Oceanic heat content in 2024 (red) versus average (blue) in the Gulf of Mexico and Caribbean Sea. Image: Dr. Brian McNoldy, UMiami.

There are two key implications to the lack of decent fronts during this AWOL fall. First, the seasonal cooling of the Gulf and Caribbean has been arrested. Total oceanic heat content of the Gulf has slightly increased in the last three weeks, hovering around mid-October norms; the heat content of the Caribbean remains well above what it would typically be at the peak of the season in mid-September. There’s plenty of fuel available to sustain a hurricane, if atmospheric conditions allow.

And allow they seemingly will. The second implication of the unusual pattern is that persistent amplified ridging over the Southeastern U.S. has displaced vertical wind shear associated with the subtropical jet stream, which usually slams the door on Gulf hurricane activity in November, to well north of its typical location.

Historical Florida landfall locations in October and November, 1851-2023.

During Rafael, this ridge was so strong that it protected the U.S. Gulf Coast, deflecting the hurricane westward to a slow, harmless death. However, this go-round, the steering wind pattern progression is a close match with the pattern preceding historical October landfalls on the Florida Gulf Coast, which are common. Florida has been struck by 38 hurricanes in October versus just three in November since 1851. In practical terms, it’s still October out there.

Click here for the latest satellite loop of Invest 99L.

The area to watch is a tropical wave merging with yet another Central American Gyre located in the Caribbean Sea near Jamaica, which the NHC has tagged as Invest 99L. This system is generating plenty of deep convection as it consolidates several low-level swirls into a single circulation, and is expected to become a tropical depression by late Thursday and a tropical storm by Friday as it moves westward towards Honduras. The next name on the list is Sara, which replaced the now-retired Sandy.

The real uncertainty in the forecast comes over the weekend, when the system will be stuck between a dip in the jet stream over the western Atlantic and a ridge to its northwest, and thus moving slowly near Central America. If the center of the low can avoid moving over land, upper-level winds are very favorable for intensification, and a strong hurricane would probably result. However, the center will more likely than not nudge southward into Honduras on Saturday or Sunday, thanks to the powerful ridging along the Gulf Coast, which would keep intensity in check. This could go either way, and what happens this weekend will make a big difference to eventual Florida impacts, so stay tuned.

Sunday evening GFS and Euro ensemble member lows, showing members splits between center locations over water and over land. (TropicalTidbits.com)

Early next week, models are in good agreement that the Gulf ridging will slide east as the first respectable cold front since mid-October pushes into the Mississippi Valley. This means whatever is milling about Central America or the western Caribbean at that time, be it a formidable hurricane or a sloppy gyre low, will move northwest and north into the southern Gulf. The center could cross the Yucatan peninsula on Monday or Tuesday as this turn occurs, an important consideration as continued favorable environmental conditions mean land interaction is the only real e-brake to intensification through Tuesday. That would come at a cost, as slow motion over land will trigger serious, life-threatening flooding in Central America.

06z Euro tropical cyclone steering wind speed and direction forecast (with surface lows) through early Tuesday, showing a the approach of a trough early next week. (CyclonicWx.com)

By late Wednesday, whatever form this storm takes is likely to accelerate northeastward across the Gulf and approach Florida or the Florida Straits from the west. If it has spent days over land, that could mean a less-defined low merging with the front, with impacts mostly in the form of enhanced showers and thunderstorms across the state. If it has spent no or limited time over Central America, a legitimate hurricane threat to the Florida peninsula is realistic. Most likely, that conditional threat would focus on Southwest Florida or the Keys, with the potential for crossover impacts in Southeast Florida, as in 1999’s Irene or 2005’s Wilma.

Overall, the possibility of a record-tying fourth Florida hurricane landfall of the year as the honeyed pipes of Mariah Carey already resound from the hard tile floors of our malls just seems wrong. Rare events are rare for a reason, and there is a good chance that land interaction with Central America can tamp down eventual impacts for Florida into the frontal low or tropical storm-like range—mostly rainfall, a possibility of severe thunderstorms. However, that outcome is not guaranteed. The October game of a track all or mostly over water could mean October prizes for Florida in the form of a significant hurricane threat in the middle of next week.

Will the hurricane season that refuses to die plunge us into one more Hurricane Hell Week out of pure spite? It’s possible, though perhaps not the most likely outcome at this point. Keep watching the skies.

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Next update: A paid subscribers-only bulletin will be out tomorrow morning, continuing our comprehensive daily coverage of this threat for supporters that began last week. (Free subscribers, click the upgrade button below to get these forecasts in your inbox each day). Next update for all is tentatively scheduled for Friday.