US Sweats Under Early Heat Wave, But Storms Love It

(June 29) -- While tropical storm worries have, understandably, stolen the headlines lately, another significant weather story has been taking place in June: intense, widespread, early-summer heat for a large portion of the U.S.

Temperatures in June have averaged four to six degrees above normal from the central and southern Plains to the mid-Atlantic region, accompanied by midsummer-like humidity. What's more, this early-season heat and humidity reflects an overall weather pattern that's favorable for tropical storm and hurricane development.

(Image courtesy of the Climate Prediction Center)

High temperatures have consistently been in the middle 90s or above, with the mercury even hitting 100 degrees (a record) in Washington, D.C., on June 24. Fifteen of the past 16 days in Memphis, Tenn., have had high temperatures of at least 95 degrees.

Once the heat arrives, especially in the southern part of the country, residents begin to accept and adjust to it, but prolonged heat like this is more common in July and August than in June.

The broiling temperatures are being produced by a large high-pressure system in the upper levels of the atmosphere and a high-pressure system over the eastern two-thirds of the country -- a pattern that's also favorable for hurricane formation. (Unlike winter storms, hurricanes need to have the relative calm of a high-pressure system over them to develop.)

In addition, the intense humidity so early in the season is, at least in part, a reflection of the warmer-than-normal sea surface temperatures in the Gulf of Mexico, which are also favorable for hurricane development. Warm water adds more moisture to the air than cool water does, so the humidity is higher along the Gulf Coast -- and areas influenced by a southerly flow from the Gulf of Mexico -- because of the warm water.

A southward dip in the jet stream out of Canada into the northern part of the U.S. will take the edge off (or completely erase) the heat from the mid-Atlantic region into parts of the South during the next few days, but this appears to be the exception to the rule. The high-pressure system will regain strength again next week, returning to a pattern similar to June's.

All of which means that this summer may be remembered for both heat and hurricanes.