Non-Tropical Low Forms Over Northeast Gulf of Mexico

A non-tropical low pressure system formed over the northeastern Gulf of Mexico on Sunday.  The low pressure system is currently designated as Invest 98L.  At 2:00 p.m. EDT on Sunday the center of Invest 98L was located at latitude 28.4°N and longitude 85.5°W which put it about 100 miles (160 km) south-southwest of Apalachicola, Florida.  It was moving toward the east at 8 m.p.h. (13 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 1009 mb.

The low pressure system formed along a frontal boundary that stalled over the northeastern Gulf of Mexico.  It is not usual for low pressure systems to form along stationary fronts.  A source of positive vorticity to provide counterclockwise rotation and upper level divergence to pump away mass and allow the surface pressure to decrease will generate a surface low.  The low pressure system does not have a warm core in the middle and upper levels and it is still associated with a frontal system.  So, it is classified as a non-tropical low pressure system.

The low pressure system will be moving through an environment that will be only marginally favorable for a transition to a tropical or subtropical cyclone.  The Sea Surface Temperature in the northeastern Gulf of Mexico is near 30°C.  So, there is plenty of energy to support the formation of a tropical cyclone.  However, an upper level ridge over the central U.S. and a trough over the northeastern U.S. are combining to produce northerly winds of 40 m.p.h. (65 km/h) over the northeastern Gulf of Mexico.  Those winds are generating significant vertical wind shear.  The shear has limited the development of thunderstorms in the northern half of the low and it may be tilting the vertical structure of the low toward the south.  The strong upper level winds will also inhibit divergence on the northern side of the low and they could make it difficult for a warm core to develop in the middle and upper levels.  The air north of the frontal boundary is drier continental air, which is another a negative factor for transition to a tropical cyclone.  Based on all of the environmental factors the National Hurricane Center is indicating that there is a 30% chance the low could make a transition to a tropical or subtropical cyclone.

The low pressure system is moving a little to the south of due east.  A strong surface high pressure system over the eastern U.S. is now pushing the front toward the south as a cold front.  The low is moving slowly eastward along the front.  Combination of the southward motion of the front and eastward motion of the low produces a forecast motion of a little south of due east.  On its anticipated track the low pressure system could reach the west coast of Florida in 24 to 36 hours.  So, the low has about a day, if it is going to transition to a tropical cyclone over the Gulf of Mexico.