Tropical Update: Looming Threat in the Atlantic?

Stu Ostro
Published: August 20, 2014

- Tropical Atlantic still stable and uneventful; disturbances trying to develop but not successfully yet; latest one we're monitoring now in central Atlantic

- A few systems in the eastern Pacific, with tropical moisture expected to stream toward the southwest U.S.

- West Pac still quiet


What a difference 24 hours makes. Mainly in terms of the ebb and flow of weather model cycles which love to play on our meteorological heartstrings. Fortunately we have the here and now to ground us. Monday night, we were watching two ill defined areas of low pressure. Now, we're still watching two ill defined areas of low pressure.

This isn't to downplay the possible development of Invest 96-L, the broad spin of clouds about 1,000 miles (give or take) southeast of Puerto Rico. But with social media posting snapshots of nine-day forecasts and bowling balls of spin rolling into the Gulf of Mexico, it's easy to lose the forest for the trees. In a sense the safest place to be is at the end of a 9-day weather forecast.

So why is this one striking such a chord? Well it's late August. It's the time of year when strong hurricanes can form. Camille and Katrina, two of the strongest hurricanes on record, were both August storms. But it's also the expected westward movement, thanks to a sprawling ridge of high pressure to the north, that will guide 96-L across the Lesser Antilles and into the Caribbean this weekend, that gives us more pause for concern.

One thing we do know: the islands of the eastern Caribbean, including Puerto Rico and the U.S. Virgin Islands, will be impacted by (at least) heavy rainfall and squally weather by late week into Saturday. The verdict is still out on whether 96-L could organize into a tropical depression or tropical storm before then, but the ocean and atmosphere ahead won't exactly discourage it.

By Friday a dip in the jet stream off the U.S. east coast will begin to pinch off the high pressure steering, at which point 96-L, or whatever comes of it, could begin to feel a little tug northward from a channel carved out by the jet stream. On the other hand, it could continue plodding westward through the central Caribbean and toward the Gulf of Mexico if the channel isn't strong enough or the system stays weak. This fork in the road wouldn't occur until late weekend into early next week, five or more days from now at which point our forecasting ability begins to drop off.

Bottom line: it's far too soon to say what if any impacts 96-L might have on the mainland U.S. Given the general steering pattern and overall favorable conditions ahead it's at least one to watch over the next few days. But first we need to see how and if it organizes tomorrow into Thursday.


Karina and large Lowell are still spinning at sea.

The two could engage in what's known as the "Fujiwhara effect" in which each affects the other's steering.

While there's a plume of moisture all the way from the tropics, the flash flooding in Arizona today is primarily due to an upper-level low pressure system over California helping to focus and enhance moisture/lift in the atmosphere beyond a typical summer monsoon day.  By Thursday and Friday models are still showing at least a bit of mid-upper level moisture originating more from Lowell itself reaching north of the border.  

The system that was near Panama yesterday and is a little farther west hasn't yet become better organized but is expected to do so, and track not too far from the coast of Mexico.  If it becomes a tropical storm, the next name on the eastern Pacific list is Marie. 

(MORE: Glossary of Tropical Terms | New NHC Storm Surge Maps)


Still a nice lull.


Our live wall below has the latest updates from our hurricane experts and from coastal National Weather Service offices. No need to refresh, the latest updates will appear at the top of the wall. Time stamps on each post are in Eastern U.S. time.


MORE: Hurricanes From Space (NASA Satellite Images)


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