News•July 1, 2014

90-Degree Days Late Arriving for Boston, NYC

Boston and New York City could see their first 90°F day of the summer Tuesday or Wednesday — unusually, if not unprecedentedly, late into the season. Not that we’re complaining.

“It’s not every year that you see us get this late” in the summer without hitting 90°F, said Joey Picca, a meteorologist with the National Weather Service office in Upton, NY. In fact, since recordkeeping in Central Park began in 1869, only 19 years, including this one, have failed to see a 90°F day before the end of June, Picca told Climate Central.Post by US National Weather Service New York NY.

Prevailing upper air patterns have kept both Boston and New York City from sweltering so far this summer, but summers overall have been heating up across much of the country under the influence of global warming. Under the scenarios with the highest future greenhouse gas emissions, the entire Northeast would see heat waves increase in frequency, intensity and duration, according to the National Climate Assessment released in May.RELATEDSummertime Blues? U.S. Seeing Red as Temps Rise
Climate Change Is Increasing Extreme Heat Globally
Map Shows When Summer Heat Peaks in Your Town

In an average year, the Central Park weather station records its first temperature of 90°F or higher on June 3. The latest date for such a temperature came on July 26, 1877, (when it hit 92°F) and the earliest date was April 7, 2010, (90°F) according to NWS records. In stark contrast to this year, the first 90°F measurement for the station last year was made on May 30.

Similarly, the station at Logan International Airport usually records its first 90°F reading of the year on June 4, on average. The latest 90°F day in the record books there was July 30, 1947, and the earliest was April 7, 2010. Last year, the city hit 90°F on May 31.

Both cities have been kept comparatively cool this year by an upper level wind pattern that has allowed cold fronts to keep sweeping in from the northwest and clearing out any warm, humid air that tries to settle in from the south.

“We’ve seen that repeatedly” this summer, Picca said.

Of course, when those warm air masses came in, they did raise temperatures close to the 90°F mark. Both Boston and New York have seen temperatures of 89°F, which might feel like an academic distinction when you’re walking down a sunny city street.

Still hasn't hit 90 degs in #Boston this spring or summer. We're now approaching the top 12 latest occurrences. #MAwx pic.twitter.com/1STkFnjOrP

— NWS Boston (@NWSBoston) June 27, 2014

And while the stations at Central Park and LaGuardia International Airport in New York haven’t topped 90°F, the one at John F. Kennedy International Airport has — it hit 91°F on June 18. The same winds from the northwest that generally keep temperatures in the region depressed can cause Kennedy to be a little warmer because they blow in from over the hot city, Picca said.

That pattern that has kept heat waves at bay is starting to break down, said NWS Boston meteorologist Bill Simpson, and both cities will likely be getting into patterns that are more typical for this time of year. Like most of the rest of the eastern part of the country, both New York and Boston see their highest temperatures in mid-July.

As warm, moist air moves in over the next few days, both cities could flirt with their first 90°F measurement of the summer. If Boston doesn’t hit 90°F Tuesday, it will tie for the year with the 12th latest 90-degree occurrence. If it fails to reach that mark Wednesday, the year will tie for 11th place.

The most recent year that saw such a late 90°F was 1985 in both places, and most of the top 12 years for Boston occurred before the 1960s.

In general, summers across the U.S. have warmed by 0.4°F per decade since 1970. Summers are warmer now in every region except the Midwest, though that is overall one of the fastest-warming places in the country. So whether or not temperatures have been tamped down in New York and Boston this summer, both cities face warmer summers in the future.