With the month of August now finished, we can look back on the warmest March-August period on record (both spring and summer are the hottest in over 120 years of record keeping). The question is – will this anomalously warm weather continue through the remainder of astronomical summer? To find the answer, let’s examine pattern trends/persistence, global teleconnection indices, and other forcings from the Atlantic and Pacific.

Generally the Northeastern US experiences the most influence from Atlantic SSTA in the month of September, when SST’s are the warmest, steering currents tend to be weaker, and more SLY winds dominate overall. If we note the current Atlantic multidecadal oscillation (AMO) picture, we’re well into the positive territory as waters are quite mild from the tropics, up the east coast, and into the north atlantic.

Another interesting factor is the north atlantic oscillation (NAO), which has been predominately negative over the past 6-8 months. Normally in the cooler season, a negative NAO corresponds to lower heights/temperatures in the Northeastern US. However, often times at this time of year – late August / September, we see the Greenland blocking “hook up” with the SE ridge upstream. Thus we have a situation where higher than average heights encompass much of the Eastern US, extending NE into the Atlantic and usually western Europe. Model proggs indicate a continued -NAO in the medium to long range.

Note the following 8-10 day ECMWF and GFS height anomalies for the globe. A few important things that stand out:

1) Ridging in the Far East, Aleutians south of Alaska, and Europe. High heights in these regions all teleconnect to ridging in the Eastern US.

2) The La Nina event in the tropical Pacific is still intensifying, and the map we see below is a fairly classic strong la nina pattern, with cooler temperatures in the Rockies/Pac NW, and warmer air in the East, Europe, and Far East.

3) Cold in the arctic. Arctic oscillation (AO) values are generally neutral to positive, meaning low heights dominate that region. This lends further support to ridging in the East.

Looking ahead to next week, I believe another heat wave could be a possibility. We’ll have a brief 1-2 day cool shot, which has been the theme of this entire summer (very few days with below normal mean temperatures), then 588dm heights begin roaring back east by Tuesday of next week. It likely won’t be as extreme as the current heat spell (difficult to beat – several days with 95 degree highs); however, there’s certainly potential for another 3+ 90F days. The best chance at this is probably Tuesday through Friday of next week. The center of the upper level ridge will be a few hundred miles further south, so the core of next week’s heat should be the TN/MS valleys into the Mid-atlantic, with 90s as far north as NY/PA/NJ and possibly southern new england (there may be backdoor potential there).

We’ve gone from the year without a summer (2009) to the year of the endless summer (2010); I’m sure most of us will have had our fill of warm weather by the time October rolls around. Evidence is strong for a warm September. In addition, I anticipate more heavy rain opportunities as we head throughout September. The drought should start to be eroded as the anomalously warm Atlantic does its dirty work. Moisture from the ocean, either indirectly or directly related to tropical cyclones, should become more common. Hurricane Earl’s rain shield will be pasing very close to our shoreline – and still needs to be watched for westward tending. However, at this time, significant impacts should not be expected.