Is Our First Tropical System Brewing?

Posted: May 7, 2015, 3:50 pm by bmarmo

For those who like to follow tropical weather, you know that the official hurricane season doesn’t start until June 1st. However, it looks like this season could be off to an early start in 2015. As conditions become more favorable over the next day or two, we will be watching for tropical development just off the Southeastern Coast of the US.

While development this early in the year is rare, it is not completely unprecedented. There have been a few systems to reach tropical storm (sustained winds greater than 38 mph) status during the first 10 days of May. Occasionally, these early season storms will exhibit both tropical and non-tropical characteristics, and are called subtropical cyclones. A subtropical storm is more favored to form this time of year as it has a lower minimum threshold for sea surface temperatures than tropical storms.

It actually hasn’t been that long since a storm has developed this early. On May 9th, 2007, a non-tropical low strengthened into Subtropical Storm Andrea about 150 miles northeast of Daytona Beach, Florida. While Andrea did not make landfall across the US, it did have sustained winds of 60 mph. In 1981, Tropical Storm Arlene developed on May 6th. Arlene was an interesting storm as it originated from tropical disturbance that crossed from the Eastern Pacific into the Caribbean Sea.

Above average sea surface temperatures (SSTs) are present off the Southeast Coast. Courtesy of ESRL (Earth System Research Laboratory)

Despite only being early May, conditions are relatively favorable for development compared to the average year. Tropical systems need warm ocean temperatures in order to form. Currently, sea surfaces temperatures off of the Southeast Coast are running above average for this time of year. In addition, wind shear across the region has gradually been lessening. A high amount of wind shear is an enemy tropical development, and thus decreasing amounts will result in a more favorable environment. If subtropical or tropical storm status is reached, which is now looking more likely, the first name on the list for 2015 would be Ana.

Relatively low amounts of wind shear off the Southeast Coast by Friday morning will result in a more favorable environment for development. Courtesy of Tropical Tidbits.

So if Subtropical or Tropical Storm Ana comes into fruition, what can be expected for our area? Right now, the likely track would take the storm up into the Carolinas. As for the Northeast and Mid-Atlantic, any impacts would be very minimal, with just increased amounts of cloud cover and perhaps a few spotty light showers or areas of drizzle for the upcoming weekend and early next week.

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