The first heat wave of the season is on the way! If your location is 90 degrees Fahrenheit or higher for three straight days, then you have a heat wave on your hands. Whether the Philadelphia and New York City metropolitan areas achieve that feat is not important for today as with temperatures already in the 70’s in the Philadelphia metropolitan area, someone will be well past 90 degrees this afternoon.
With the warm front finally well to the north of the northern Mid Atlantic, located in northern New England, a hot and humid air mass on the back of a southwesterly wind at all levels of the atmosphere has invaded the Philadelphia and New York City metropolitan areas. Winds will be from the southwest at 5 to 10 mph by this afternoon. Locally dense fog this morning will lift by 10 AM and give way to scattered clouds. An isolated thunderstorm will be possible, but not likely in the afternoon and evening as weak mid level disturbances passes by. The thunderstorm will be capable of heavy downpours, wind gusts over 40 mph, and frequent lightning. Temperatures will rise into the lower to mid 90’s over all of southeastern Pennsylvania, the Delaware River Valley, and the immediate western suburbs of New York City; upper 80’s to lower 90’s over the northern interior, the five boroughs of New York City, and coastal Connecticut; mid 80’s to lower 90’s over coastal New Jersey; and mid to upper 80’s over Long Island.
Similar conditions can be expected tonight on through Sunday as the same air mass and upper level pattern locks in over the Eastern United States. Each passing day will feature more humidity leading to a heat index pushing close to if not passing 100 degrees. Isolated afternoon showers and thunderstorms will be a threat due to the natural instability in the atmosphere and pesky mid level disturbances moving around the mid and upper level ridge. These thunderstorms will feature heavy downpours, frequent lightning, and wind gusts over 40 mph. I am concerned about the threat for localized flash flooding and down burst wind damage due to these thunderstorms. Meanwhile, locally dense fog will be a threat each morning with visibility in some locations below a mile. Temperatures will remain well above normal. Low temperatures will range from the mid to upper 60’s over the interior and upper 60’s to mid 70’s along the coast. High temperatures will range from the lower to mid 90’s over the Philadelphia metropolitan area, upper 80’s to lower 90’s over the New York City metropolitan areas, and mid to upper 80’s along the immediate coast.
A strong cold front will move through on Monday with widespread showers and strong to severe thunderstorms. These thunderstorms will be capable of very heavy downpours, wind gusts over 50 mph, frequent lightning, and hail. Temperatures will depend on the timing of the cold front. The later the cold front moves through, the warmer the atmosphere will be. Temperatures will range from the mid 60’s to lower 70’s for lows and mid 80’s to lower 90’s.
A cool, Canadian air mass will invade the region with high pressure in complete control on Tuesday and Wednesday. Temperatures will still be slightly above normal however the humidity will be much lower. Low temperatures will range from the mid to upper 50’s. High temperatures will range from the upper 70’s to lower 80’s along the coast and lower to mid 80’s elsewhere.