Aug 5, 2011: Heavy Rain Possible On Sunday

With a high pressure just off the coast, today brought more of a south wind into the area, with temperatures slightly warmer than those of yesterday, reaching the mid 80s inland, lower to mid 80s in the immediate NYC area, and the upper 70s to lower 80s across Long Island and southern Connecticut. Temperatures will slightly warm up tomorrow, but cloud cover will increase as well as a low pressure approaches the area, bringing a heavy rain risk.

Weekend Outlook:

Tomorrow will bring increasing clouds, starting with partly cloudy skies becoming cloudy by the afternoon hours. Temperatures will be similar to those of today with a south wind expected again, reaching the lower to mid 80s from NYC and further west, and the upper 70s to lower 80s in Long Island and southern Connecticut.

By tomorrow night, however, rain will begin to move in from the west as a low pressure approaches the area. High precipitable water values are expected, between 2 and 2.5 inches, which will support locally heavy rainfall with the storm. The rain will be the main risk from this storm, as rainfall amounts as high as 2-3 inches are possible in the areas that see the heaviest rain. At this time, it appears that the heaviest rain axis will be from the NY/PA border towards southern New England, also covering the northern half of the area. At this time, I am expecting a total of 1 to 2 inches for the northern half of the area, and 1/2 to 1 inch for the southern half of the area, but these totals are not final yet and are subject to change. It is possible that most of the rain ends up staying to the north of the area, as some of today's model runs have been showing.

Following the scenario currently expected, rain will move into the western parts of the area around tomorrow evening, and into the eastern parts of the area during the early overnight hours. The heavier rain is expected to develop after at least 2-4 AM, and should last through Sunday morning. The rain is then expected to end by Sunday afternoon with mostly cloudy skies and an isolated shower or thunderstorm. This scenario is not final, as previously mentioned, and other scenarios will bring less rain into the area. High temperatures will then rise into the lower to mid 80s from NYC and further west, and into the upper 70s in Long Island and southern Connecticut, where showers will continue through the mid afternoon hours.

Next Week: Scattered Storm Risk Continues

There is some uncertainty for Monday, as some of the latest models trended in a direction which would bring a hot, humid and potentially stormy scenario into the area. Tomorrow night's low pressure will already be offshore, but another low pressure is expected to move through New York, which may put the area in the warm sector of the storm. Should this scenario verify, temperatures will surge into the upper 80s to lower 90s from NYC and further west, with humid conditions which would bring the heat index well into the 90s. This is still uncertain, however, and at this time, I went with a scenario where the front stays close to the area, bringing temperatures into the mid to upper 80s from NYC and further west, potentially reaching the 90 degree mark in parts of NE NJ, and the lower 80s in Long Island and southern Connecticut. More information will be posted on Monday's scenario with tomorrow's update.

With Monday's cold front expected to move south of the area, Tuesday will bring slightly cooler temperatures, back into the upper 70s to mid 80s across the area, and while an isolated thunderstorm is possible in the late afternoon/evening, especially north and east of NYC, the probability of rain is lower than that of Monday. Wednesday may bring slightly warmer temperatures along with the risk of scattered thunderstorms, and it appears at this time that Thursday/Friday may bring a break from the rain, with more sunshine and drier conditions. Stay tuned for more information on next week's forecast.