Down to One in the Atlantic

After a run of 5 hurricanes in less than two weeks, it’s down to Invest 94L tracking toward the easternmost Caribbean islands this week

After its most active start to October on record and following a spate of 5 hurricanes – including 3 major hurricanes – in less than 2 weeks, the Atlantic is throttling back to a more reasonable pace for middle October.

The only game in town this week will be Invest 94L, a low-pressure swirl spinning harmlessly westward through the open Atlantic between Africa and the Caribbean. 94L is moisture-starved and will likely struggle to ignite much in the way of organized showers and thunderstorms for at least the next few days while it stays in a dry environment.

By middle to later this week, however, conditions may become more conducive for modest development as it moves near or north of the easternmost Caribbean islands. Given the trajectory in the vicinity of the Leeward Islands, it’s worth watching for those with interests or travel plans in the eastern Caribbean.

Odds of the low-pressure center associated with Invest 94L passing to within about 100 miles of any given location from our most reliable global forecast models. Models generally steer the system near or north of the islands for Friday into the weekend then either ricochet it northward or dissipate it west by early next week. Credit: Tomer Burg/University of Oklahoma

For now at least the consensus lifts the system far enough north by Friday and Saturday to avoid any direct entanglements with the islands – including Puerto Rico and the U.S. Virgin Islands – but we’ll want to follow the trends this week for any southern shifts.

Is Invest 94L a problem for the mainland U.S.?

It’s still a little early to speculate whether 94L could slip far enough west to be a troublemaker for the U.S. but right now the odds aren’t in its favor.

Historically, hurricanes to hit the mainland U.S. this deep in the season have come from the western Caribbean, not the Atlantic. Only four U.S. hurricane hits beyond mid-October have originated from systems forming east or north of the Caribbean: Unnamed (1887), Hazel (1954), Kate (1985), Nicole (2022).

Of course, that isn’t to say it couldn’t happen, but it’s increasingly unlikely past mid-October for a system of deep Atlantic origins to affect the U.S.

For 94L, if tracking north of the Caribbean, it would not only need to continue westward – a difficult feat in the waning days of the subtropical high steering – but would also need to survive a curtain of wind shear descending across Florida and the waters bordering the continental U.S. as fall cold fronts begin to clear the Sunshine State.

Wind shear departure from average from this Thursday, October 17^th through next Tuesday, October 22^nd from the European forecast model ensemble system. Models are advertising very hostile wind shear across Florida and into the western Atlantic for the time frame 94L will be approaching, limiting long-term development prospects closer to the mainland U.S. Credit: TropicalTidbits.com

October is a month South Floridians should continue to be vigilant, but we typically look for late-season issues from the south like where Milton and Helene had their starts, not to the east and north, where 94L is coming from.

We’ll follow the trends over the next few days, but for now it’s not something we need to worry ourselves with stateside.

In general, the Atlantic’s transitioning to a less conducive state than it’s been in for development the past few weeks. The Madden-Julian Oscillation or MJO that helps to regulate tropical activity throughout the season will be in a more suppressed state for the next few weeks.

Areas of rising (blue/cool colors) and sinking (red/warm colors) air straddling the equator (between 15°N and 15°S) by global longitude (x-axis) from middle September (top of the chart) through November 14^th (bottom of the chart). The time vs. longitude chart is known as a Hovmöller diagram and shows the global progression of weather features. The forecast chart shows the rising air that’s been favoring development (part of the Madden-Julian Oscillation or MJO) in the Atlantic since the last few weeks of September has transitioned to sinking air (outlined area), which should largely suppress development until the rising branch returns by the end of October or beginning of November. Credit: ECMWF

The MJO may try to make one last pass to revive things as the calendar turns to November, but it will be facing stiff climatology headwinds at that point. Historically 95% of hurricane season activity is behind us by the start of November.