Sea Breezes: Thunderstorm Makers or Destroyers?

 

The last time I wrote a blog, I talked about thunderstorms in Florida and that Florida is the lightning capital of the United States in part because we have sea breezes nearly every day in the spring and summer that help to initiate thunderstorms. Well, as you might have seen from the comments that followed that column, one very smart and observant weather weenie said, Joe, how can that be? How can sea breezes help to cause thunderstorms in Florida, but weaken and destroy thunderstorms in places such as Long Island and coastal New England? Having grown up on Long Island and watched many a thunderstorm weaken and dissipate before reaching my backyard, I could certainly identify with that question.

 

I believe the answer has to do with the temperature of the water in Florida versus Long Island, and with the amount of moisture in the air and the stability of the atmosphere over Florida during the summer. Consider this: as the sea breeze develops during the morning in Florida, the temperature of the water, either in the Gulf of Mexico or the Atlantic Ocean, is generally in the upper 70s or 80s. The land heats up quickly and the air temperatures over the land may rise into the low or even middle 90s. So, there is maybe a 10-degree difference in the temperature of the air behind and ahead of the sea breeze. That may not seem like a whole lot of difference, but there is enough of a density difference between the two air masses to create a boundary with a wind shift, and that is enough to initiate thunderstorms. In addition, the dew point temperatures are generally in the low to perhaps middle 70s, and so that is plenty of fuel to aid thunderstorm development. Also, the atmosphere up to 30,000 and 40,000 feet over Florida is almost always close to unstable. Given the heating of the day, and the convergence of air masses provided by the sea breeze, there is good reason for thunderstorms to develop.

 

Now consider the situation on Long Island, or along the New England coast. In May or June the air over the land can heat up very quickly and it can certainly get into the 80s and even the 90s at points that are well away from the shore. The water temperature is probably in the 60s. That would appear to be plenty of temperature difference to initiate a pretty strong sea breeze, and indeed it does. There were many days in the spring and summer that I watched my thermometer in Hewlett, N. Y., on the south shore of Long Island climb into the 80s by noon and then drop back into the low 70s during the afternoon. As that sea breeze moves northward and westward, it does cause clouds to form, and if the moisture content of the air is high enough, showers or thunderstorms can form. I have seen that happen in July and August when dew points are in the 60s to near 70, but earlier in the spring there usually just isn't enough moisture in the air, and the overall weather pattern is just too stable to initiate thunderstorm development. So, sea breezes in Florida can and do initiate thunderstorms on a daily basis, but farther north on the coast the phenomena becomes rarer. In addition, they can quickly weaken and become very unimpressive when very impressive squall lines from the west hit the cool sea breezes in the spring and early summer in the Northeast. As a weather weenie growing up on the south shore of Long Island, I watched many a squall fade, and don't get me started about how the warm ocean water in the winter frequently turned a promising snowstorm into rain ... grrrrrrrr. The ocean is great to be near, as evidenced by the millions of people moving to the shore every year ... but to a weather weenie, it can be a cruel task master at times!!!!



By Dr. Joe Sobel - http://www.accuweather.com/

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