Summer Heat And El Nino

Boston's maximum temperature yesterday failed to attain 90 degrees again. The atmosphere supported 91 for the high but it is possible that residual smoke from the Canadian wildfires plus a rather wet ground from recent rains contributed to the failure. In any event, the wait for the first 90-degree day of the season continues.

2015 is now in 6th place for the longest wait for 90 degrees.  With the present expectation that an onshore breeze will blow for the next week or more, Boston's temperature doesn't have a chance at reaching 90 until at least July 20th. Thus, on the 21st, 2015 will move up to 3rd place! For those who worship the heat, it is rather disappointing.

For the rest of us, we are relieved that excessive heat has been absent the last two summers. The main driver is the positioning of the pools of warmer and cooler than average sea-surface temperatures. The "+" anomaly in orange and red over the eastern Pacific linked with the "-" anomaly in blue and green over the north Atlantic are working in tandem to produce the cooler regime here in the Northeast. This prompted us to predict a very cold and snowy winter of 2014-15 and a near to below average summer of 2015. There is no sign that this present SST regime in the oceans is about to change soon. Typically, the Pacific pools of warm water in one location have lasted no more than two years before migration or cooling takes place. Interestingly, the June sea surface temperatures for the whole Atlantic were the second lowest(coldest) on record. The warmth in the eastern Pacific maintains a mean ridge of high pressure over the western portion of the country and more downstream troughing in the eastern portion of the country out over the Atlantic. Unlike other summers, strong ridging is suppressed over the eastern seaboard for now. As a result, brief spells of hot weather are interrupted by building masses of continental air streaming out of central Canada into the upper Midwest and Northeast.

Note in the SST Anomaly Map above the ribbon of heat in the equatorial central and eastern Pacific indicative of a rather strong El Nino. How is this El Nino going to impact our changing weather here in the Northeast? The impact should be minimal this summer but 2016 could be a different story. At this time, this is a strong El Nino but according to Joe D'Aleo  and Joe Bastardi of WeatherBell, it is about half as strong as the very strong El Nino of 1997-98 but stronger than the moderate El Nino of 2009-10.

Boston only received 8 days at 90 or higher in 1998 during that very strong El Nino of 1997-98 while there were 24 days at 90 or higher in 2010 during the moderate El Nino of 2009-10. In 1988, Boston had 25 such days during the strong El Nino of 1987-88 and more than a whopping 30 days during the very strong El Nino of 1982-83.

Can we conclude that next summer will be a very hot one like 1988 or 1983? Not necessarily. The strength of the El Nino does not always dictate the magnitude of the summer heat here in New England. While El Nino can be a huge driver in our climate, there are other global factors that must be examined to determine which ones will rule or trump the others. It is a complex mix of sets and subsets composed of a myriad of atmospheric and oceanic oscillations.

For now, it appears that Boston will not have any 90-degree days until the last 7-10 days of the month. Present clues suggest that the mean temperature for August and September will be close to a bit below average but that doesn't mean there couldn't be a few days at 90 or higher. I will stick with my projection revealed back in April that Boston would have around 8-12 days at 90 or higher through September. We shall see.

In the short term, the humidity will be high right into Wednesday with drier air taking over Thursday through Saturday. There will be some showers and a few boomers scattered around especially on Tuesday and Tuesday night. Presently, the threat of severe weather seems low this week.

Make it a great week!