Hurricane season in the Atlantic basin begins on June 1st, but there are some signs of the season’s first tropical or subtropical cyclone this coming week. That chance for the first tropical disturbance will take place close to home in the eastern Gulf of Mexico.
What is a subtropical cyclone? This is the official definition from the National Hurricane Season: “A non-frontal low-pressure system that has characteristics of both tropical and extratropical cyclones. Like tropical cyclones, they are non-frontal, synoptic-scale cyclones that originate over tropical or subtropical waters, and have a closed surface wind circulation about a well-defined center. In addition, they have organized moderate to deep convection, but lack a central dense overcast. Unlike tropical cyclones, subtropical cyclones derive a significant proportion of their energy from baroclinic sources, and are generally cold-core in the upper troposphere, often being associated with an upper-level low or trough. In comparison to tropical cyclones, these systems generally have a radius of maximum winds occurring relatively far from the center (usually greater than 60 n mi), and generally have a less symmetric wind field and distribution of convection.”
A washed-out frontal boundary has moved north from the Caribbean to the Florida Peninsula, bringing days of heavy rain and thunderstorms to most of the state this weekend and into the Southeast much of next week due to a constant flow of moisture coming in from the south.
In the upper-levels of the atmosphere, a low pressure is expected to form over the Gulf of Mexico by the end of this weekend. It will then deepen and strengthen through mid-next week before it is expected to move into the northeastern Gulf Coast by Thursday the latest. While this happens, a surface low pressure is appearing more and more likely to form on Monday. This low will slowly track to the north, and is expected to move onshore on Wednesday.
Two of the ingredients that these kinds of tropical systems need in order to develop are low wind shear and warm sea surface temperatures. In terms of wind shears, it does appear that there will be a window of lower wind shear over the eastern Gulf of Mexico at the start of the week. Sea surface temperatures will be on the cooler side but they are near average for this time of the year. Portions of the Gulf are featuring temperatures as low as 76 degrees, but typically tropical cyclones rely on temperatures of at least 80 degrees.
According to the European model, the latest run suggests there is up to a 30% chance for tropical or subtropical depression development early next week. This storm will be very weak and the main threat is heavy rain despite whether it develops or not. This model also highlights a near-zero percent chance for tropical or subtropical storm development.
This storm system will be very weak if it develops, but it’s important to know that hurricane season is fast approaching and it is worthwhile to prepare now so you’re ready if a storm threatens later this year.