All Weather News

A Named Storm in the Atlantic?

25 Mar 2017, 9:52 pm

It may be March but we’re keeping our eyes on an area of disturbed weather in the tropics!

Satellite (white) with satellite-derived radar reflectivity (green/yellow) of unsettled weather near the Bahamas

The image above shows our in-house product here at WeatherNation called the satellite-derived radar reflectivity. You’re looking at clouds, showers, and even some thunderstorms to the east of the Bahamas. No, this isn’t an organized tropical storm or hurricane, but for now it is an area of distrubed/unsettled weather. However we’re closely watching it because there is *a chance* that this becomes a subtropical system Sunday, Monday, or Tuesday.

A subtropical system? What’s that? Unlike tropical systems which have a warm core and operate in light vertical wind shear environments, subtropical cyclones are associated with weather fronts, aided by the upper levels and jet streams, and are *usually* weaker. A subtropical system can still produce very strong wind and very large waves. So will this form into a subtropical or tropical system? It’s hard to say for sure, but it is a possibility. It’s unlikely to form into a tropical system, but subtropical…maybe.

Sea surface water temperatures near where this unsettled weather is festering

In order to develop a tropical (or subtropical) system, there needs to be a fuel source. Throughout hurricane season we monitor sea surface temperatures because the warmer SST’s are, the more energy that can be pulled out for a tropical cyclone to use. Usually a rule of thumb in meteorology and forecasting is that we should look for the 25 degree Celsius line as a minimum for storm development. A reading of 25C would equal 77 degrees Fahrenheit and there are SST’s close to that where this area of unsettled weather is trying to get its act together. This area is also aided by an upper level low with colder air above the warmer ocean water. That helps to generate thunderstorms and possibly a subtropical low.

Wave heights on Saturday night as gale force wind began

Regardless of (sub)tropical formation, windy and wavy weather can be expected for the Bahamas and eventually for Bermuda. Waves could rise up to 12 feet within the disturbed area, up to 8 feet closer to the Bahamas and Bermuda shorelines. For Bermuda, that would be more likely Monday or Tuesday. Let’s take a look at how weather models grasp the future with this system.

Sunday’s surface map showing surface winds with isobars
Monday’s forecast with forecast wind speed and direction along with isobars

This particular weather model, the GFS (aka American) shows a closed circulation with wind speeds reaching up to 50 mph. Minimum sustained winds within a tropical storm are 39 miles per hour or greater. But again, it’s the “makeup” of the weather system that classifies it as a subtropical or tropical system. Meanwhile the European model (not shown here) also shows 50+ mph winds by Monday-Tuesday.

This has no impact on the United States and is forecast to move away from the Southeast throughout the week. It would be very noteworthy if this does become a named storm, because it will be just the second time in recorded history that we have had a named storm in March. The only other (in recorded history) was in March 1908.

Regardless named or not, the impacts of this weather system will be strong wind, big waves, and mostly a threat to shipping routes and boaters in the area. The closest islands of the Bahamas and Bermuda may experience gusty showers, but will likely experience breezy winds and rough surf. If named, it would be Arlene.

For WeatherNation, Meteorologist Steve Glazier

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