Gulf of Mexico Development Possible; Flood Threat Regardless

Jon Erdman
Published: October 18,2015

We're getting late in the 2015 Atlantic hurricane season, but one area of disturbed weather over the Gulf of Mexico in the week ahead will be monitored closely for potential tropical development. Even if this system does not develop into a tropical cyclone, we are still concerned about a heavy rain and flood threat in parts of the South starting late this week.
(MORE: Expert Analysis | Hurricane Central)

Watching the Western Gulf

For now, a broad area of thunderstorms is percolating near Mexico's Yucatan peninsula, associated with a tropical wave, not yet showing signs of organization.

Enhanced Satellite, Surface Pressure

This tropical wave and associated cluster of thunderstorms will migrate only very slowly west-northwestward into Monday, leading to locally heavy rainfall and flash flooding. The low pressure center is currently over land and is not expected to emerge over water, which makes development less likely.
(FORECASTS: Cancun | Cozumel)
There is a chance that the disturbance then glides west-northwest through the Bay of Campeche and western Gulf of Mexico later this week.
Meanwhile, the subtropical branch of the jet stream will be in play from northern Mexico into much of the Deep South of the U.S.
If winds aloft are favorable for intensifying thunderstorms, but not too strong over the western Gulf of Mexico, it's possible a tropical depression or tropical storm could form there sometime in the week ahead.
Given the configuration of a deep southward jet stream dip in northwest Mexico and higher pressure aloft to its east, this system would then get drawn northward toward the western or northern Gulf Coast sometime next weekend.

Setup in the Week Ahead

If, however, the southern-branch jet stream is too strong over the western Gulf of Mexico, thunderstorms and the heat generated by condensing water vapor within them, would be blown away from any surface low trying to become a depression, effectively squelching tropical development.
This wind shear is a common nemesis of both developing and active tropical cyclones and has played a significant role already with several named storms this hurricane season.
A key point is that you do not necessarily need a named storm to produce significant impacts. We explain why we are concerned about a potential flood threat later this week below.

Heavy Rain, Flood Threat Regardless of Development

Regardless of tropical development, this atmospheric pattern should set up a significant surge of deep, tropical moisture into parts of the western Gulf coast, southern Plains and possibly the Lower Mississippi Valley late in the week ahead.
Bands of locally heavy rain may trigger flooding, and persistent onshore winds may lead to some coastal flooding, high surf and rip currents, as well, by the latter half of the week ahead.
(FORECASTS: S. Padre Island | Corpus Christi | Houston | Lake Charles, Louisiana)

Rainfall Outlook

This rain is needed to help a relatively rapidly-developing flash drought, which set in over the southern Plains and Lower Mississippi Valley from mid-summer on.
(MORE: Drought Has Returned Again)
The heavy rain threat, while squelching the recent wildfires, may be "too much of a good thing" in these areas, instead triggering flash flooding. It's also possible some of the drought area may see little or no rain at all from this setup.
Interestingly enough, the western Gulf of Mexico isn't exactly a late October hot spot for tropical development.
Since 1950, only one named storm has formed in the western Gulf of Mexico during the last 10 days of October: Hurricane Juan (1985), whose meandering path near the northern Gulf Coast lead to major flash flooding, particularly in the state of Louisiana.
The more typical late October active tropical cyclone track is from the western Caribbean Sea to South Florida, near the Southeast U.S. Coast, or eastward to Bermuda.
(MORE: Where the October Hurricane Threat is Greatest)

Origin points of Atlantic named storms from Oct. 21-31 from 1950-2014.

On average, one more named storm and one more hurricane form in the Atlantic Basin from October 20 until the season's end.
Again, while development is not imminent, check back with us at The Weather Channel and weather.com for the latest on this tropical disturbance.