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Disturbance? Subtropical? A likely rainmaker, regardless of label

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Posted at 4:30 PM, May 11, 2018
and last updated 2018-05-11 12:36:48-04

MIDWAY, Fla. (WTXL) -- With the beginning of the 2018 Atlantic hurricane season less than three weeks away, it's natural for attention to start focusing on waves of moisture and systems that originate south of our area, instead of cold fronts from the north that become less frequent.

Mumblings about disturbances in the Gulf -- one early next week, another the following week -- have raised suspicions about the chances that the region can experience a tropical hassle even before the hurricane season starts June 1.

While it's not necessarily unusual to have pre-season tropical activity, the system forecast to impact the eastern Gulf early next week will be mainly a rainmaker, with limited expectations for anything organized.

A patch of moisture is lingering in the southernmost Gulf of Mexico, waiting for high pressure draped over Florida to nudge eastward.  A pattern of swift upper-level winds over the Gulf will influence the development of a large, upper-atmospheric low, which will help transport the moisture field north toward the Florida peninsula this weekend.

As Monday and Tuesday approach, this broad low will generally advance north toward the northern Gulf coast.  This would cause the moisture plume to spread even farther north, creating more cloud cover and periods of rain that can be heavy at times.

The upper wind pattern through this period is capable of triggering the development of a low-pressure center, which would accompany the disturbance in its journey toward the northern Gulf.  However, considering the marginal set-up present in the Gulf (cooler water surface temperatures and fast upper-level winds), a purely tropical low is unlikely to form.

If the disturbance's wind field is strong enough, and a counter-clockwise, defined, closed circulation develops, the disturbance can get a possible classification as a "subtropical cyclone."  A subtropical cyclone contains a mix of warm and cool air within it, and gets its organization from atmospheric wind trends and not so much from warm ocean waters.

Regardless of whether the system will be just a plain ol' low or a subtropical low, the bottom line is that many parts of the eastern Gulf, including sections of the Big Bend and even southern Georgia, will experience an increase in clouds starting Monday with areas of rain developing and spreading north. Early projections show chances of rain totals exceeding 1" near the tri-state, and possibly 3" for the Suwannee Valley, through early next week.

Projections of a tropical system in the Gulf during the week before Memorial Day are extremely premature. They are based on long-range models, foreseeing conditions more than 10 days in the future, that naturally have extreme margins of error.  Many computer models also can improperly indicate long-range tropical storms and hurricanes in the early phase of the season.  Unverified and non-analyzed digital media postings of such information should be taken with a healthy amount of skepticism until higher quality forecast data is produced in the next week.