Memorial Day weekend — the unofficial start to summer — is here, which means it’s time for beaches, pools and barbecues as the heat of the season sets in.

Although most of the country has been warming up as normal this spring, temperatures in the Middle Atlantic and the Northeast have been on the cool side for much of May. But this week, there’s been a sharp turnaround, with temperatures seemingly fast-forwarding to July.

So far this month, a persistent storm track from the northwest has kept parts of the East Coast cool and damp over the past few weeks. Large parts of Delaware, Maryland, and Virginia are having one of their 10 coolest and wettest Mays on record, according to the Southeast Regional Climate Center.

The recent weather in Washington, D.C., highlights this pattern: 20 of the first 24 days in May were cooler than normal there. Not surprisingly, the first 11 days of the month had rain (actually, that streak extends back to April 27). More energy is needed to warm up water than dry land, so when rain is falling or the ground is wet, temperatures are lower.

But the temperatures have snapped back and will remain above normal into this weekend, as the jet stream and its associated storm track shift north, allowing warm air to race northward. Highs soared into the 80s on Tuesday, and they will remain much more summerlike for the rest of the week.

The overall outlook for the summer is for better odds of hotter than normal across most of the country. The Climate Prediction Center indicates a lack of a clear signal in the Central Plains, so the temperature there this summer may depend on just how wet the season turns out.

Summer precipitation and temperature outlook

Summer precipitation and temperature outlook.


There is not a dominant relationship between the El Niño (or La Niña) and summer temperatures in the U.S., and even so, the current El Niño is fading rapidly, likely transitioning to La Niña later this year.  According to the CPC, the summer outlook is influenced by temperature trends in the atmosphere and oceans, and more specifically, the sea surface temperatures in the Atlantic and the Pacific.

The globe is already having its hottest year on record so far, as each of the last 12 months have been the hottest such on record. And over the last month, parts of the Atlantic and Pacific near the U.S. coast have been 1.8°-3.6°F (1°-2°C) above average. Because ocean temperatures change very slowly, it stands to reason this summer will trend warm.

SST anomaly

Sea surface temperature anomalies over the previous month. From NOAA Physical Sciences Division.


Warmer than normal oceans and La Niña also support a more active hurricane season in the Atlantic. Even though the season doesn’t officially begin until June 1, the first tropical disturbance is just northeast of the Bahamas this week. The system is expected to drift to the northwest toward the Southeast coast over the next few days, and conditions are favorable for development of a tropical storm.

If it does form, the storm would be named Bonnie. Areas from the Outer Banks of North Carolina to the east coast of Florida should probably keep an eye on that system as the holiday weekend approaches.

Watching the tropics may be an especially good idea this year, as the U.S. is well past due for a strike from a major hurricane, which is defined as Category 3 or higher. Hurricane Wilma was the last, hitting Florida in October 2005, and this has been the longest period on record without a hurricane of that intensity making landfall in the U.S. At some point, that luck will run out.