Sea surface temperature difference from normal over the Atlantic and Gulf of Mexico. (NOAA)

The western Atlantic Ocean is cooking right now. More specifically, waters off the Mid-Atlantic and Northeast coasts are unusually hot, even for August.

Case in point, the water temperature in Atlantic City was the highest on record Wednesday — a tropical 83.3 degrees.

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Coastal water temperatures throughout the Mid-Atlantic are warmer than normal. In both Lewes, Del., and Ocean City, Md., the most recent water temperature measurement was 78.3 degrees, compared with the average in the low-to-mid 70s.

The astute observer will take note that official ocean temperatures in Atlantic City only go back to 1995, leaving us with a smaller sample size than we would probably desire. Nevertheless, a record like this deserves some recognition and at the very least, some further investigation!

Why is the Atlantic so warm?

Short answer: It’s August and we should expect the Atlantic to experience its warmest annual period from now through early October. Of course, this oversimplified explanation doesn’t satisfy our scientific curiosity.


Current 500mb heights and MSLP. Via Tropical Tidbits

A quick look at the current upper-level weather pattern over the North Atlantic shows a large ridge of high pressure dominating the entire landscape. In fact, this feature is what you can blame for what’s sure to be a sweat-filled weekend.

In addition to pumping in a warm, moist air mass into the eastern half of the country, this type of set-up is also conducive to similar effects on ocean water. Namely, the dominant flow both in the atmosphere and on the ocean is from the south and southwest and from regions that have ample amounts of heat and humidity. We can see the evidence of this in the current atmospheric and oceanic flow.

Of course, while the ocean and atmosphere are closely coupled, the processes that drive their behavior are different in some significant ways. The two biggest differences between the two are size (the ocean is quite large and deep) and time (which is directly related to its size).

Simply speaking, changes in the ocean happen on a much slower time scale than changes in the atmosphere. With that in mind, we often find it more advantageous to look at temperature anomalies (monthly temperature departures from the monthly average taken between 1981-2000) when it comes to sea surface temperature (SST). As it turns out, these readings are on the warm side as well.


July 2016 monthly SST anomalies via Columbia

And if we back out even further, we notice that warm SST anomalies have been rather persistent over the past three months for large portions of the Atlantic.


Three month (May-July 2016) average persistence of above average SSTs. Via Columbia

Further investigation into the upper level pattern over the North Atlantic for the past 30 days shows a rather persistent ridge of high pressure that has done nothing to dislodge the ocean warmth.

In short, the ocean is presently warm because it’s been warm, and the dominant atmospheric pattern has only reinforced the warmth.

Implications from a warmer than average Atlantic?

So we’ve covered a little bit of the why, but what kind of sensible weather effects can we expect from warmer than average sea surface temperatures?

1) Increased atmospheric fuel: When it comes to oceans and temperature, we need to think in terms of stored energy. That is, warmer sea surface temperatures (SSTs) are able to provide more moisture content to the lower atmosphere (mainly through evaporation from the surface).

Increased moisture content in the atmosphere can have a direct correlation to enhanced instability and convection. The two are not mutually exclusive and the effects can vary in space and time, but it is fair to say that warmer ocean temperatures, especially near the coast, can act as a catalyst for an increase in rainfall and thunderstorm activity.

2) Influence on tropical storm development: Recently, the news has spread quickly about the current major hurricane drought ongoing in the Atlantic. Its been much of the same story for 2016 Atlantic tropical season as well, with not much development forecast in the near future.

However, we know that tropical systems are powered by warm ocean water and the increased abundance of such water could have implications on storm intensity should anything form later this season. Interestingly enough, CWG tropical experts Phil Klotzbach and Brian McNoldy found that seasons with higher than average SSTs in the Atlantic may induce more storm development but reduce the chance of storm impact along the East Coast.

3) An active autumn?: Yes I know, its hard to even fathom fall-like weather given today’s conditions, but signals in SST variance can have strong implications on weather conditions in the following season.

As we’ve already mentioned, the time it takes for things to change in the ocean is much slower than in the atmosphere. Therefore, it is well within reason to expect warmer than average Atlantic SSTs to last into the autumn months. The most immediate impact of this may be a more active storm track during what usually amounts to our “rainy” season. Big ocean storms love to feed off the contrast between warm water temperatures and cooler land air masses that we typically begin to see more of in the autumn.

Regardless of any potential future impacts, don’t expect the above average SSTs to go anywhere soon. And with the warm temperatures at nearby Atlantic beaches, consider it as increased enticement to head to the shore during these hot and humid dog days of August.