Yesterday's high temperature in Central Park was only 89 degrees. Technically, that means this week's warm weather is not an official heat wave. For that to happen in New York the high has to reach at least 90 for three consecutive days.
But let's not get hung up on technicalities. A high of 89 along with dew point temperatures in the 70s made for a completely miserable day. That trend will continue today as this very muggy air mass again warms up to near 90. Thanks to that combination of heat and humidity the city is under a heat advisory until early this evening.
The high humidity isn't just near the ground. The marine air mass we are under has nearly saturated the lowest 3-4 miles of the atmosphere. With that amount of moisture it won't take much of a disturbance to set off showers and thunderstorms. Lots of sun this morning should destabilize the atmosphere and an uncommon shortwave approaching from the west/back door cold front approaching from the east later in the day should be sufficient to set off some meteorological fireworks. Look out for scattered, but intense, rain showers from late this afternoon through tomorrow morning. If thunderstorms develop they could contain small hail and gusty winds.
Tomorrow is expected to still be plenty humid, but easterly winds and mostly cloudy skies will keep the temperature in the 70s. The cold front won't pass through the area until Sunday, so we've got another round of showers and thunderstorms possible tomorrow and again on Sunday morning. Once the front finally passes we should be in some cooler, drier air, with the first few days of next week looking sunny with highs in the mid 80s.