Then August hit — which has pushed the number of hot 90-degree days this summer into above-normal territory. We’ve now piled up 37 such days this year, exceeding the 1981-2010 average of 36.
Including Wednesday, the District has now seen 15 days at or above 90 in August alone, the most of any month this summer. We should end with 17. The normal is 10.
As we saw during a few blissful days last weekend, August is not July. It often sends us a taste or two of autumn ahead, as the first cold fronts with some power start reaching us again. But this year those tastes have been fleeting, and we’re ending the month with one of the hottest heat waves of the summer.
Tuesday’s heat, in particular, was notable. A high of 94 and a low of 78 produced a daily average of 86 degrees. That was good enough for a tie for the 25th-warmest day on record during the last week of August or later. We should end up with similar numbers Wednesday and, perhaps, even higher.
Heat in perspective
One reason this summer might not have seemed too harsh until recently is that the last three summers produced many more 90-degree days to this point. Recall that 2016 also had 23 days of 90 or greater in August, including several over 100. While it can be worse, this year’s 90-degree day count is within the top quarter of years for Washington back to the 1870s.
The overall trend in 90-degree days is undoubtedly upward over time. Since the mid-1970s, the count has risen by about six days.
But this summer, at least, we haven’t hit 100 — another reason its heat may not seem so extreme.
Washington’s hottest temperature this year of 98 degrees in early July was hot but not historically so. Our typical hottest day of the year is somewhere around 99 degrees. We did see a streak of eight days in a row of 90 or higher earlier this month, which topped any run from last year.
But if the heat hasn’t been intense, it has been persistent. This persistence has allowed this year to become 11th warmest on record, to date, despite no highs hitting the century mark. The summer has ranked 15th warmest on record.
The heat is really showing off at night.
Washington’s low temperature of 79 Wednesday morning tied with 1993 (when it hit 79 on Sept. 3) for the warmest minimum temperature this late in the year.
Warm overnight low temperatures have been a staple in our region and most of the Northeast throughout the summer. The maps above nicely highlight how widespread these extremely warm lows have been.
Boston meteorologist Eric Fisher tweeted that Wednesday morning’s low of 81 degrees at Logan Airport was the warmest low in that city so late in the season, by a number of weeks. It was also the second-warmest low on record there, in any month, he noted.
The heat goes on
Now that we’ve notched 37 90-degree days, how many more should we expect? From here until the end of the heat season, Washington tends to pick up about three to four more such days. We should easily do that this year.
Although the Mid-Atlantic and Northeast might get a brief break in intense heat heading into the weekend, a ridge of high pressure is expected to expand again early next week. This should mean more 90s for many.
In Washington, the continuation of warm-to-hot temperatures should get us to reach and surpass 40 days at or above 90-degrees this year. How far past is still to be determined. Our biggest adversary when it comes to piling up more days is probably the calendar.
Although there is no hint of a major cool-down anytime soon, and, in fact, September looks pretty warm for now, average high temperatures are starting to fall rapidly and are already down to the mid-80s. That fact, thankfully, means 90s are on borrowed time. They’ve certainly already overstayed their welcome.