Battle for Delaware: Air masses clash along a summertime sea breeze

Earlier this year, Don Lipman pointed out that a breeze off the water can turn an early-season beach weekend into something less enjoyable than planned. But, come mid-summer, the result is often welcome relief from suffocating heat.

Related: D.C. heat wave 2013: 10 red hot maps

With thermometer readings soaring into the mid-90s across much of the D.C. area and broader region on Tuesday afternoon, even locations close to the cooler ocean were baking.


A sea breeze possibly enhanced by the shape of the Delaware Bay pushes into Delaware on Tuesday, July 16. (Weather Underground)

As the radar loop above shows, it was a prime day for an impressive summer sea breeze. Land temperatures in the 90s, which heat much quicker than water, were as much as 30 degrees warmer than the adjacent ocean.

A sea breeze gets going when warm air rises off the land, and cooler denser air over the water runs inland to fill that void. The warm air is eventually transferred back out over the water high above the surface, before eventually cooling once again, thus sustaining the sea breeze circulation.

Observations from Dover, Delaware before and after the sea breeze passed show its impact well:


Hourly observations from Dover, Delaware. *Click for larger* (Weather Underground)

Prior to the sea breeze passing, Dover was seeing winds predominantly from the north just like most of the Mid-Atlantic. Behind the sea breeze, those winds shifted to east southeast, and ultimately slowed.

Temperature relief was considerable — with readings falling 10 degrees pretty rapidly (some drop probably associated with sunset). On the flip side, humidity levels also rose significantly, with an hour-to-hour jump of over 5 degrees, up into the mid-70s.

Sometimes, when the conditions are right, a sea breeze can be a conduit for thunderstorm development. This is more often seen in places like Florida during the summer.

No storms formed with the sea breeze yesterday, probably thanks in part to the mega upper level high pressure over the region. As you can see below, visible satellite didn’t even pick up on the boundary at all.

Visible satellite loop from 4:30 until 8 p.m. during the same period as the radar loop shown above. No major signs of the sea breeze are present though clouds along the New Jersey coast and change in cloud movement is some signal. (NASA)
Visible satellite loop from 4:30 until 8 p.m. during the same period as the radar loop shown above. No major signs of the sea breeze are present though clouds along the New Jersey coast and change in cloud movement is some signal. (CWG adaptation of NASA imagery)
Ian Livingston is a forecaster/photographer and information lead for the Capital Weather Gang. By day, Ian is a defense and national security researcher at a D.C. think tank.
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Dan Stillman · July 17, 2013