Sept 12, 2013: Storms Today, Much Cooler Weekend

Forecast Highlights:

gfs_namer_045_850_temp_mslp_precipA brief yet significant heat surge affected the region yesterday, with temperatures climbing into the low-mid 90s and heat index values into the 100s. While temperatures will cool down today, another relatively hot and humid day is expected away from the coast, with a cold front bringing a line of rain and thunderstorms for the evening. A much stronger cool air mass will return behind the front, with below average temperatures persisting through the middle of next week.

<< September 10 | September 11 | September 12 >>

Wednesday, September 11 Observations:

9.11.13An unseasonably warm and humid air mass spread into the area, with 850mb temperatures near 20C and mostly sunny skies leading to July-like heat across the area, with highs peaking in the low to mid 90s away from the coast, with highs in the mid-upper 80s in SE CT and western Long Island and the low-mid 80s in eastern Long Island. Along with dew points in the mid 70s, peaking as high as 77 degrees in Montgomery, NY, heat index values reached the 100-106 degree range across most of the area away from the coast. The highest temperature was 97 degrees in Teterboro, NJ, and the coolest high temperature was 80 degrees in Montauk, NY.


Records set/tied on Wednesday, September 11:

Bridgeport, CT – high temperature
90 degrees (tied record: 90 degrees – 1983)

Islip, NY – high temperature
88 degrees (tied record: 88 degrees – 1989)



Today – Friday: Storms, Then Cooling Down

Yesterday’s hot and humid air mass moderated, with slightly lower dew points and temperatures aloft cooling down to at least 18C, which along with increased cloud cover and some storm coverage will lead to slightly cooler temperatures than yesterday, peaking in the mid to upper 80s away from the coast, where highs in the low to mid 80s are expected. Latest observations from the Weather Prediction Center (WPC) show several cold fronts in the Ohio Valley and Michigan regions, with the most notable front moving through the area late this evening. With moderately favorable instability and bulk shear parameters, a line of heavy rain and strong to locally severe thunderstorms is expected to develop in New York and Pennsylvania states this afternoon, then gradually track east; scattered storms are possible north and west of NYC in the afternoon hours, which could be capable of heavy rainfall and strong wind gusts, with the line of storms reaching the area towards the evening hours, likely weakening as it passes east of NYC but still capable of producing moderate to locally heavy rainfall.

Behind this front, temperatures will cool down overnight into the 60s across the area with decreasing humidity, with partly sunny skies, a breezy NW wind at 10-15 mph, and highs reaching the low 70s inland and the low to mid 70s for the rest of the area. The strong trough will enter the region overnight with 850mb temperatures falling to nearly 4C, but with the high pressure staying to the west keeping some cloud cover in place, along with the pressure gradient behind the departing cold front keeping a breezy northwest wind, overnight lows are likely to struggle falling below the upper 40s to low 50s away from NYC and the coast.


Weekend – Next Week: Chilly Through Mid Week, Then Warming Up

Tropical Storm Gabrielle has weakened into a tropical depression near Bermuda, and is likely to continue struggling to intensify over the next day as it accelerates to the north and NNE ahead of the cold front. By Saturday morning, its remnants are likely to merge with a developing low pressure near eastern Maine, which then moves northeast into Atlantic Canada, allowing the high pressure to build into the region. Mostly to partly sunny skies are expected on Saturday with highs ranging from the mid 60s inland to near 70 degrees in NYC, with overnight lows falling into the low 40s inland, mid to upper 40s in the north/west suburbs, upper 40s to low 50s in Long Island, and the low to mid 50s in NYC and the coast. Mostly sunny skies will continue into Sunday with highs in the low 70s across most of the area.

Another trough will quickly move in on Monday behind the previously existing one, with even cooler temperatures expected to follow the frontal passage. Highs on Monday are expected to range from the upper 60s inland to the low-mid 70s near NYC and further east, with lows at this time forecast to fall into the upper 30s inland, mid 40s in the north/west suburbs of NYC and southern CT, mid to upper 40s in Long Island away from the coast, and upper 40s to low 50s in NYC and the coast. Some models indicate the possibility of lows under 50 degrees in NYC; the last time NYC had a sub-50 degree low in September was in 2009. Mainly sunny skies will continue into Tuesday with highs reaching the upper 60s to low 70s range again.

The last medium range outlook on September 6 noted that the large scale pattern is generally shifting towards ridging in the eastern half of the US, which was originally likely to occur after the 15th, but with the possibility of another trough on the 17th delaying it by a few days. The early week trough will keep chilly temperatures through the 18th, but the pattern is still expected to trend towards ridging in the eastern half of the US beyond mid next week as the trough axis shifts into the western US, where a persistent trough is likely. A warmer pattern will develop over the central US, with highs returning into the upper 80s to low 90s range, while the region will be near the edge of the ridging, with a back door cold front possible on the 19th, which would keep temperatures near to slightly below average but with no widespread cool down likely at this time. Depending on the exact pattern setup, high temperatures may return into the 80s during this time frame, but the widespread heat as the region is currently seeing with widespread upper 80s and 90s is likely done for this year.

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