Humidity drops midweek, but only briefly

The warmest day of the year occurred in early September, yesterday in fact, as the high in New York City’s Central Park reached 92 degrees. More than the date of the temperature, the actual temperature of 92 degrees being the warmest of the season may be even more shocking. Despite ending around average temperatures for meteorological summer, this calendar summer has featured a peculiar lack of 90+ degree days in NYC (only 5) and no days over 95 F. Granted, there is some variance between Central Park and areas to the west-southwest, but the general idea remains the same.

The humidity is another story — and it made Tuesday’s hot weather even more unbearable. Heat index values approached the upper 90’s with dew points near the 70’s. Generally soupy and humid weather was uncomfortable for anyone who spent a period of time outside. Wednesday, however, features a much less humid and somewhat cooler airmass. Highs in the lower 80’s will feel much more comfortable as a result of this.

NAM model showing highs returning to the upper 80’s on Thursday.

The cooler and more comfortable airmass will only be temporary, however, as mid level heights will begin to rise ahead of a trough over the North-Central United States. Temperatures at 850mb will noticeably rise again by the end of the week, approaching 20 C by Friday. The warm air will return on Thursday, with highs in the mid to upper 80s, but dew points will remain fairly comfortable.

The sensible weather on Thursday will differ greatly by location. Models agree on the offshore circulation forcing the development of southeast winds near the area shores. This means an increased likelihood of a developing seabreeze — and cooler temperatures near the coasts. The inland push of this seabreeze won’t have any inhibitors, so it may mean a push of low clouds and a breeze even into the interior by evening. Still, inland areas will rise into the upper 80’s before this occurs. Later in the evening, winds will back from Southeast to West-Southwest.

It won’t be until Friday and Saturday when the uncomfortable, humid and sticky air will return. Highs near 90 are expected on both Friday and Saturday as a southerly flow takes over. Dew points are forecast to increase into the upper 60’s to low and mid 70’s by Friday. Heat index values will approach the mid 90’s once again, and a summery feel will return to the air.

Saturday will break the heat and humidity once again, as a disturbance approaches from the west. Showers and thunderstorms, some strong, are expected after temperatures warm toward 90 in the afternoon with uncomfortable humidity values. The volatile pattern, again, looks to continue through the medium range with bouts of heat and humidity followed by showers and storms every few days.