The Squalls of March
During the early afternoon hours of Thursday, March 10, 2011, the leading edge of a large area of rain, showers, and thunderstorms swept rapidly southward through the Florida Keys and adjacent coastal waters. Winds shifted from light southerly to north at 30 to 40 knots in a matter of minutes, with peak gusts of 45 to 50 knots. Blinding downpours immediately followed the wind shift, and air temperatures plummeted 10°F in less than 15 minutes. A menacing shelf cloud signaled the onset of the heavy weather, as it rushed southward. A “shelf cloud” is a low-level, horizontal, wedge-shaped cloud associated with a thunderstorm’s gust front. The shelf cloud is attached to the storm’s cloud base. Air currents rise in the leading (outer) part of the shelf cloud, while the underside appears turbulent and tattered. The sudden onset and intensity of wind and rain caught many boaters off guard, and local marine response organizations (U.S. Coast Guard, Florida Fish and Wildlife Conservation Commission (FWC), Tow Boat U.S. and other partner agencies) responded to 15 separate search and rescue cases in less than two hours. Multiple small boat crews from Coast Guard Station Islamorada, Coast Guard Station Marathon, and Coast Guard Station Key West, a helicopter aircrew from Coast Guard Station Miami, and numerous partner agency vessels were involved in the responses.
Weather-related marine incidents associated with this “March squall” included the following:
- Several boats throughout the Florida Keys went adrift after their mooring lines snapped.
- A 21-foot sailboat with four people aboard began taking on water near Summerland Key.
- A drifting sailboat struck power lines near the Channel Five Bridge.
- Two boats lost power near Little Palm Island.
- A boat capsized in Florida Bay, and two people were pulled from the water.
- A 40-foot catamaran ran aground, and took on water near Cottrell Key. All persons subsequently were evacuated by the U.S. Coast Guard.
- Four parachutists from Sugarloaf Airport landed in shallow water after being blown off course.
Your Florida Keys National Weather Service predicted thunderstorms along a cold front for several days prior to this strong squall event. However, squall line intensity, coverage, and movement usually are very difficult to predict with any accuracy until the event is only 6–12 hours away. The National Weather Service issues location-specific Special Marine Warnings for strong to severe thunderstorms and squalls with a typical lead time of 10 to 60 minutes. This certainly is an improvement from 10 or 20 years ago, but if you are 90 minutes from a safe harbor, then this is a problem! This is where awareness and preparedness are important, and potentially life-saving. The United States Coast Guard motto is Semper Paratus, meaning “always ready”--good advice for any mariner. Moreover, the primary vision of the National Weather Service is a “Weather-Ready Nation”. Readiness is the “state of being fully prepared for something”, and this means deliberate actions toward maintaining high levels of awareness and preparedness. Accessing quality marine weather information from your local National Weather Service forecast office is only one part of competent voyage planning and execution.
To avoid being a “search and rescue case”, please:
- Stay Informed. Check the current and expected weather and water conditions before heading out (weather.gov), and be aware that weather conditions can change quickly.
- Wear life jackets while on the water.
- File a float plan with friends, family members, and local marinas before heading out. The list should include the number of passengers aboard the vessel, destination and expected time of return.
- Always have a working marine-band radio on board.
- Carry marine flares on board the vessel.
- Ensure bilge pumps are operational and vessels are secure for heavy winds and rain. Have a manual pump on hand as a backup.
Squall season is here. Please be marine weather-ready, and stay safe!
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Chip Kasper
Author
Chip is a senior forecaster and marine program meteorologist at the NOAA/National Weather Service Forecast Office in Key West. The National Weather Service provides weather, water, and climate information for the protection of life and property on land and at sea. Email Chip at kennard.kasper@noaa.gov.