Historically speaking, late July is when New England experiences its hottest weather. August usually begins the slow decline in average temperatures. Boston's average temperature drops four degrees from the start of the month to the end. This means that by August, the hottest day of the year is typically in the past. That looks to be the case this year.
TEMPERATURES
August is off to a generally cool start, particularly in northern areas. The first day of the month will see highs in the 60s and lows in the 40s across the northern tier. The rest of the region will be slightly below average to around average for the first week of the month.
Heading into week two (August 6-12), temperatures are looking to moderate back to around average, which is the low 80s for most in New England. Full summer heat will likely continue to be elusive as North Atlantic Oscillation (NAO) dives back negative after nearing neutral conditions.
A negative NAO favors generally cooler and more unsettled weather over the eastern United States while a positive NAO is the opposite. It needs to be emphasized that these are general trends. Just because NAO is negative doesn't automatically mean it will be cool. Take late July as an example, despite NAO being negative, New England saw a ridge in the jet stream that caused heat advisory level warmth.
A better way to look at it is that a negative NAO will limit big time warm ups, and the ones that do occur will be short lived. New England has been in a negative phase for pretty much the entire summer. Big time warm-ups this summer have generally been short lived with most lasting a few days or less before reverting back to around average.
Boston has yet to experience a heat wave this summer (three consecutive 90+ degree days). This trend will likely continue to be the case through at least mid-August, and very well could persist into late-August. There are signs of NAO trending back to neutral conditions by mid-August, but by then, intense summer heat becomes less likely under any circumstances.
There are indications of a ridge in the west (which a negative NAO favors) for at least the first half of the month (favored by a positive PNA, which acts the same as NAO, just for the west). It is looking like the coolest of the temperatures (relative to average) will remain to New England's west. That will allow New England to generally be seasonable.
The NOAA's 8-14 day outlook (covering August 8-14 at this time) shows the same general temperature outlook as the 6-10 day outlook above, just with a notch less confidence, which is expected when forecasting further out.
Just like last month, there are signals pointing toward a warmer second half of the month (relative to average). Overall, southern New England will have the better chance to be above average in August. This is a flip from June and July, when northern New England saw better odds. We're predicting another very average month overall, with upper 70s to mid 80s dominating.
RAIN
A negative NAO also favors a continuation of unsettled weather. Low pressure systems are looking develop across the country's midsection and track northeastward. This has been the pattern as of late. Low pressure systems have been tracking to New England's north, leaving northern areas generally wetter. This looks to continue with an area of low pressure tracking to New England's north this Friday dragging a cold front across the region.
This general northern track of low pressure systems will keep northern New England in the greater chance for above average rainfall. This can be seen on the NOAA's 6-10 day precipitation outlook. The entire region does look to remain above average rain-wise.
The big question will be how often is New England hit by a storm system, and, more importantly, how quickly (or slowly) will these systems move through the region. As of late, these systems have sped up, allowing longer dry times between systems.
TROPICAL ACTIVITY
August and September are prime time for tropical cyclones to make landfall (or have an impact on the region without making landfall) in New England. Henri (2021), Irene (2011), Bob (1991), Diane (1955) and Carol (1954) all impacted New England in August. Historically speaking, it's unlikely for a tropical cyclone to make landfall in New England under any circumstances, but with a negative NAO and troughing, it will be even less likely this month. The window for a cyclone to squeeze into New England will be very small (but not shut completely, there is never a 0% chance).
LOOKING BACK
Everything in our July outlook panned out as expected. We predicted 80s dominating for highs with brief warm-ups. Boston, Hartford, Manchester and Burlington all saw over half of all days in July top out in the 80s. There were also warm-ups that didn't last for a week (or weeks) at a time, but rather a few days.
We also predicted above average rainfall, and we all know how that ended up playing out with a handful of events dropping multiple inches of rain in places. Our Weather Wednesday episodes published on July 5, July 12 and July 19 all led off with flooding issues in New England.
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