Tropical Threat May Brew by Mid-June
It’s just one week into the 2021 Atlantic hurricane season, and meteorologists are watching the tropics with a particularly close eye on the waters surrounding Central America. AccuWeather forecasters say the potential exists for the development of a tropical depression or storm — one that they have been scrutinizing for the past week — and the chances will grow in middle to late June.
A phenomenon known as the Central American Gyre is anticipated to develop in this area later this week and this weekend.
An atmospheric gyre is a large circular zone of lower air pressure that slowly spins. The Central American system can encompass thousands of square miles and sometimes overlap waters in the western Caribbean, the eastern Pacific, and even the southwestern part of the Gulf of Mexico.
This broad low-pressure zone typically makes it easier for clusters of drenching showers and thunderstorms to develop. It is where these clusters linger over warm waters that tropical disturbances can gradually evolve into tropical depressions or storms.
An uptick in showers and thunderstorms over Central America, southern Mexico, and some of the islands in the western Caribbean, in general, is likely to result from the pattern this weekend and into next week.
This image, captured on Monday, June 7, 2021, shows no organized features over the western Caribbean, the Gulf of Mexico, and Central America. (CIRA at Colorado State/GOES-East)
“The formation of this gyre would also raise the chance for tropical development in the northwest Caribbean, the southern Bay of Campeche or off the west coast of Central America on or around June 15,” AccuWeather Hurricane Expert Dan Kottlowski said.
Strong wind shear will likely be an inhibiting factor much of this week over the western Caribbean and Gulf of Mexico, as has been the case thus far this season.
Wind shear is the increase in speed or change in direction of breezes at different layers of the atmosphere above the sea surface or across the sea surface in the horizontal. When wind shear is strong, it tends to inhibit tropical storm formation or cause an established tropical system to weaken.
“Wind shear is expected to diminish over the western Caribbean Sea late this week and weekend, which may allow the increased thunderstorm activity to gradually organize and form an area of low pressure,” AccuWeather Senior Meteorologist Rob Miller said.
“Provided wind shear remains low, this low-pressure area may slowly develop into an organized tropical system in the northwestern Caribbean Sea or southwestern Gulf of Mexico this weekend to next week,” Miller continued.
It was around the same time last year that the formation of the Central American Gyre contributed to the formation of Tropical Storm Amanda along the coast of El Salvador over the Eastern Pacific on May 31, 2020.
Amanda moved ashore later on May 31 and then dissipated over southern Guatemala. However, part of the moisture and wind field left over from Amanda gave birth to Tropical Storm Cristobal along the coast of Mexico’s Yucatan Peninsula in the southwestern Gulf of Mexico, which is considered to be in the Atlantic basin.
Cristobal June 2020 Satellite Loop (NOAA / AccuWeather)
Cristobal moved northward across the Gulf in the following days and made landfall as a tropical storm in southeastern Louisiana on June 7.
The 2020 Atlantic hurricane season went on to become the most active on record with 30 named systems that included 14 hurricanes. There were a record 12 landfalls in the United States. For comparison, an average hurricane season yields around 14 named storms, with about seven that go on to strengthen into hurricanes, based on data over the 30-year period from 1991 to 2020.
While AccuWeather meteorologists do not expect the 2021 Atlantic hurricane season to reach the same number of named systems like 2020, this season is expected to be very active and well above-average, with the potential for several direct impacts on the U.S.
It’s not out of the question with the upcoming pattern for a tropical storm to develop and then move into the Gulf of Mexico during the second half of June. The track of such a feature toward the western or central Gulf Coast could be detrimental in terms of rainfall and potential flooding, especially in areas of Texas and Louisiana that have been hit hard with up to 2 feet of rain in recent weeks.
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