A cyclone is likely to form over the Gulf of Mexico during the upcoming weekend. A broad area of low pressure at the surface is currently centered over the Yucatan Peninsula. The area of low pressure is currently designated as Invest 90L. The circulation around the low pressure system is not well organized at the current time. The center of the surface low is over the Yucatan Peninsula. Showers and lower clouds are occurring near the center of the low. Stronger thunderstorms are occurring on the eastern side of the low over the northwestern Caribbean Sea. Sustained winds of 20 m.p.h. to 30 m.p.h. (30 km/h to 50 km/h) were blowing across the northwestern Caribbean Sea. The winds were weaker over land near the center of circulation.
An upper level trough over the Gulf of Mexico was producing strong westerly winds which were blowing over the top of the surface low. Those winds were causing strong vertical wind shear and the wind shear was one of the reasons why the stronger thunderstorms were occurring east of the center of circulation. Sinking motion in the western portion of the upper level trough was bringing drier air to the surface and the drier air was inhibiting the formation of thunderstorms in the western side of the surface low.
The National Hurricane Center (NHC) indicated in a Special Tropical Weather Outlook at 2:00 p.m. EDT on Thursday that there is a 70% probability of the formation of a subtropical or tropical depression during the next 48 hours. NHC has tentatively tasked a reconnaissance aircraft to investigate the low pressure system on Friday afternoon if necessary.
The wind speeds are slower near the axis of the upper level trough. If the surface low pressure system moves under the axis of the upper level trough, then there would be less vertical wind shear and a cyclone could form. If thunderstorms develop near the center of circulation after the center moves over the northwestern Caribbean Sea or southeastern Gulf of Mexico, then NHC would likely designate the system as a tropical depression. If the thunderstorms develop farther away from the center of circulation and the circulation does not exhibit a tropical appearance, then NHC could classify the system as a subtropical depression. NHC would issue advisories on the cyclone even if it is designated a subtropical depression.
There is a strong high pressure system over the Atlantic Ocean and the high is likely to steer the surface low toward the north. The Sea Surface Temperature of the water in the southeastern Gulf of Mexico is near 27°C. So, there is enough energy to support the formation of a tropical cyclone. Most of the stronger thunderstorms are likely to continue to form in the eastern side of the circulation because of the vertical wind shear and drier air to the northwest of the surface low. The low pressure system could slowly organize into a tropical storm during the weekend.
Heavy rain and the potential for flooding are the greatest risks with this low pressure system. There will be some storm surge along the eastern and northern coasts of the Gulf of Mexico as counterclockwise rotation around the low blows water toward the shore.