Francine will be third hurricane landfall on the US Gulf coast this year

Shortly after my post on Monday, Francine did indeed form, and then was upgraded to the season's fourth hurricane on Tuesday night.  It is nearing Category 2 hurricane intensity, and will make landfall in Louisiana tonight.  Elsewhere, a strong easterly wave out near Cabo Verde could become Gordon by this weekend.

The NHC's experimental version of the "cone of uncertainty" graphic shows inland wind-related watches and warnings, removes the border around the cone, and eliminates the dotted treatment of the Day 4 & 5 part of the forecast... all-around some really nice improvements.

Of course, in addition to the wind-related watches and warnings, there are storm surge watches and warnings too, and as of the Wednesday morning forecast, a peak storm surge of 5-10 feet is possible from Intracoastal City over to Port Fourchon.  Tide schedules vary within this region, but water levels will be maximized if the peak storm surge arrives at or near high tide.

As mentioned in the title of the post, Francine will be the third hurricane to hit the northern Gulf coast already this year (Beryl and Debby were the others).  That's a lot... though there were five in 1886, four in 2020, 2005, and 1985... and three in 1934, 1915, 1888, and 1860.  So it's not unprecedented, but it's unusual and certainly not welcome! Oh, and the season's not over yet.

Once Francine makes landfall it will continue to move inland and weaken, dumping some hefty rain totals along the southern Mississippi Valley before rather quickly dissipating.  You can find the rainfall forecast maps (and other hazards) on NHC's website at https://www.nhc.noaa.gov/graphics_at1.shtml?start#contents

NHC has four other areas of interest highlighted for potential development in the coming week, but the only one I'll discuss here is the one presently near Cabo Verde... the others have very low probabilities of becoming tropical cyclones.

That wave, tagged as Invest 93L, exited the African coast on Monday and has a lot of model support for development very soon.  Persistent thunderstorm activity is located in a relatively small portion of the broad circulation, and it appears very close to becoming the season's 7th tropical cyclone.

As of now, global model ensembles indicate a west-northwest track for the next 5-6 days followed by a turn to the north somewhere near 50°W longitude (well before the Lesser Antilles).  They also suggest it will struggle to intensify too much until that north turn, after which it could become the season's 5th hurricane. At any rate, as of right now, it does not appear that future-Gordon will be a threat to land.

Catching up on the progress of the season's activity as measured by ACE, even with Hurricane Francine out there, 2024 is struggling to keep up with climatology... right at 98% of average for September 11.  Of course, there's still half of hurricane season ahead of us, and all indicators continue to point to it being above-average.

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Soon-to-be-Francine threatens northern Gulf coast this week

It has been an eerily quiet three weeks since advisories ended for Ernesto on August 20, but at the flick of a switch, the tropical Atlantic is lightning back up with activity.  There is a disturbance brewing in the southern Gulf of Mexico and a couple easterly waves east of the Lesser Antilles that I'll discuss here.  The next three names on the list are Francine, Gordon, and Helene.

The system in the Gulf of Mexico, tagged as "Potential Tropical Cyclone Six" is close to becoming the season's 6th named storm, Francine, and poses a threat to the northern Gulf coast later this week.  It's currently a bit disorganized, but model guidance is confidently showing a quick increase in organization today.  The latest NHC forecast for this disturbance (a tropical cyclone has not formed yet) tracks it northward along the far western Gulf, reaching the coast sometime on Wednesday afternoon, likely as a hurricane. Remember: the cone itself does not show impacts, only a historic 2/3 likelihood of where the center of the storm will track.

On that trajectory, it will pass over a patch of extremely anomalously high ocean heat content tomorrow.  In addition, sea surface temperatures along its path are 30-31°C, so the ocean under future-Francine is primed to fuel and sustain anything.  The ocean heat content averaged over the entire Gulf is the highest it's been on record for the date. 

NHC forecasts it to become the season's 4th hurricane on Wednesday, and although its window of favorable environmental conditions is relatively brief, it appears there will be an opportunity for rapid intensification from midday Tuesday through midday Wednesday.

Regardless of exactly how much it's able to intensify in the next couple of days, the potential for significant flash flooding from heavy rainfall is there over parts of the southern US.

Now for a quick briefing of the two easterly waves in the deep tropics between the Caribbean and Africa.  Both of these have been given a 60% probability of forming within the coming week by NHC, and both are expected to continue tracking toward the west-northwest.  Since neither of these pose a threat to land through early next week (slim chance of Leeward Islands this weekend), we'll just keep an eye on them as see how they evolve this week. The long-range model guidance is not too bullish on either of them. But given the time of year, every disturbance in the deep tropics warrants some attention.

This week is the climatological peak of hurricane season, and although we have no named storms right now, that's likely going to change quickly.

Looking at the season's overall activity in terms of ACE (Accumulated Cyclone Energy), even if Francine does form today, 2024's ACE will slip a hair below the climatological value for the first time since June 29. But based on NHC's forecast, that will be rectified by tomorrow and 2024 will be back above average.  This time of year it takes a decent amount of activity just to keep pace with the average.

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Hurricane Ernesto to impact Bermuda on Saturday

Since my previous post on Monday morning, Tropical Storm Ernesto did indeed form later that day, becoming the season's fifth named storm.  The center passed over Guadeloupe then the Virgin Islands, dumping hefty rainfall totals over the Leeward Islands and Puerto Rico.  It was upgraded to the season's third hurricane on Wednesday morning, centered just northwest of Puerto Rico.

As I wrote on Monday, the intensity model guidance continued to indicate it would reach Category 3 intensity as it neared Bermuda, and the official NHC forecast now includes that as well.  Once it gets closer, you'll find a long, updating radar loop from Bermuda at https://bmcnoldy.earth.miami.edu/tropics/radar/

There's very little spread in the track guidance.  It will pass over or near Bermuda on Saturday morning, gradually weakening in the face of increasing wind shear by then, then continue north toward Newfoundland.  A turn toward the east is likely at some point near Newfoundland, so any impacts there would depend greatly on how soon it starts heading east.

Although it won't be a tropical cyclone anymore, a potent extratropical cyclone could then reach the UK next Thursday-Friday.

One long-distance impact that these powerful hurricanes over the open ocean create is substantial wave and swell action... the east coasts of the U.S. and Canada will experience elevated threats of coastal flooding over the next six days due to Ernesto, which also aligns with amplified tides due to a full moon coming up on the 19th.

The climatological date of the third hurricane formation is September 7, and the climatological date of the second major hurricane formation is September 19.  Not suprisingly, this season is wayyyy ahead of schedule by those metrics, as well as by ACE, which is ~304% of average for the date.

The basin continues to look quiet for the foreseeable future after Ernesto, but now that it's mid-August, we should enjoy this relative calm while we can.

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