July 13, 2011: Excessive Heat Next Week?

Unexpected Storms Today:

The forecast for today originally called for mostly sunny skies and high temperatures in the mid 80s to lower 90s. Unlike the expectation, however, scattered thunderstorms formed and affected parts of the area, especially northern New Jersey, NYC, and parts of Long Island, bringing gusty winds and locally heavy rainfall. High temperatures were slightly cooler than expected as a result, peaking in the mid 80s inland and in the mid to upper 80s in the immediate NYC area, Long Island, and southern Connecticut. While this round of rain was unexpected, it is certain that there will be no rain tomorrow and on Friday as a high pressure moves over the area.

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As mentioned above, today brought unexpected storms into the area with cooler temperatures than expected. Tomorrow through the weekend will be dry, however, as a high pressure moves over the area, which will prevent rain from affecting the area and keep mainly sunny skies in place. This high pressure will bring seasonable temperatures as well, peaking in the upper 70s to mid 80s across the area.

With the high pressure exiting the region by Sunday, more cloud cover will return, and as the wind begins to shift more towards the south/SW, hotter temperatures will return, with 90s returning into the immediate NYC area for Monday and Tuesday before the next cold front comes through. Unlike the more recent cases, however, it is possible that the cold front may have less of an influence than previous scenarios we’ve seen, and if this scenario verifies, excessive heat may affect the area by late next week.

Thursday – Saturday: High Pressure In Control

With the cold front out of the area and a high pressure moving in, tomorrow will bring sunny skies to the area with a NNE wind expected. Seasonably mild high temperatures are expected as well, with high temperatures peaking in the lower to mid 80s from NYC and further west, and in the upper 70s to lower 80s across Long Island and southern Connecticut.
With the high pressure still in control, similar conditions will continue across the area on Friday. By Saturday, the high pressure will drift offshore, which will bring more of a SSW wind into the area. This will allow warmer temperatures to slowly return into the area, reaching the upper 80s in parts of the immediate NYC area. With the expectation for next week, however, these upper 80s may end up being some of the coolest temperatures the area sees until the last week of July.
Sunday And Monday: Heat Slowly Returns
A massive ridge will develop in the central United States during the weekend into early next week, with a widespread area of 500 mb heights above 594 dm, which indicates extreme heat with the potential for record temperatures once again in that region. Some of that heat will spread into the region as well by Sunday/Monday, with 850 mb temperatures warming up into the 16-18 degree celsius range.
As a result, Sunday will still bring mostly sunny skies to the area with highs in the mid to upper 80s from NYC and further west, with a few lower 90s possible in NE NJ, along with cooler temperatures in Long Island/southern Connecticut due to an onshore wind. Monday will bring more widespread warmth, with upper 80s to lower 90s from NYC and further west with mid to potentially upper 80s in Long Island/S CT, and a few places may get close to the 95 degree mark in the warmer case scenario.
Tuesday And Beyond: Excessive Heat?
Model/Scenario Analysis: A cold front will approach the region on Tuesday, but what this cold front does will determine the set up for the remainder of next week into next weekend. The front will be associated with a low pressure well to the north of the US/Canada border, and some models show the front failing to bring any cool down. In fact, the ECMWF model intensifies the heat, with both its early morning and afternoon runs showing potentially record heat in the region, with 850 mb temperatures in the 22-26c range, indicating temperatures reaching the 100s. The ECMWF is most likely exaggerating the heat intensity for next week, but it is possible that the front fails to bring any cool down into the area.
Meanwhile, the other models are showing more of an influence from the cold front, but the exact scenario varies with each model. The GGEM and DGEX are the likely outliers, with the DGEX developing a strong low pressure near Maine which brings a stronger cool down for a longer period of time, with the GGEM developing a coastal low, a highly unlikely solution. Both models, however, ultimately end up showing a building ridge at the end of their runs. The GFS is still showing different solutions from run to run, as should be expected in the longer range, but at this time the overall idea it has is a more reasonable one, where heat spreads into the region for Monday and Tuesday, followed by a brief and weak cool down on Wednesday. The excessive heat then builds in again from Thursday to around Saturday.
This is still in the longer range and the smaller details are easily subject to change, but when looking at the overall set up, the main factor that drives this heat wave is the center of the ridge which is modeled to shift further east, from the central US more towards the eastern US, which has not happened with most of the heat spells we’ve seen so far this summer. The ensemble means also show big heat spreading into the region, with the GFS ensemble mean showing decent agreement for hot temperatures late next week. While there is still time for changes in the expectations, at this time I am expecting hot temperatures for Monday and Tuesday, a brief cool down around Wednesday which may potentially last through Thursday at the latest, followed by a building ridge with excessive heat late next week into next weekend.
Forecast for the NYC area: Monday and Tuesday are expected to be hot days in the area, with lower to mid 90s in the immediate NYC area on Tuesday. A cold front will affect the region, bringing a risk of thunderstorms on Tuesday, but it is still too far in the future to determine how high the risk of rain actually is. As previously mentioned, I am expecting a brief cool down around Wednesday with temperatures cooling down slightly below the 90 degree mark, but temperatures should warm up late next week, reaching well into the 90s. More information will be posted on this over the next several days, including any potential changes in the forecast scenario.

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