Sept 9, 2013: Near Record Heat Wednesday

Forecast Highlights:

temp48Another brief cool down was observed today across the region, but it will quickly move out, however, with a warm front pushing through on Tuesday bringing a much warmer and humid air mass. Wednesday is expected to be one of the hottest days of the year, with near record temperatures as highs rise into the low to mid 90s away from the coast, with heat index values as high as 100 degrees. A cold front on Thursday will remove the heat while producing widespread thunderstorms, followed by a much cooler weekend with October-like temperatures.

<< September 7 | September 8 | September 9 >>

Sunday, September 8 Observations:

9.8.13Following the weekend warm up, another cold front moved through the region early in the day, with a breezy NW wind at 10-15 mph, mostly to partly sunny skies, and highs slightly warming up into the low to mid 80s across the area, except for eastern Long Island and interior locations in the mid to upper 70s. The highest temperature was 87 degrees in LaGuardia airport, and the coolest high temperature was 74 degrees in Port Jervis, NY.



Tonight – Thursday: Hot, Humid Wednesday; 100 Degree Heat Index Possible

nam_namer_000_850_temp_htPattern Overview: After an inactive pattern for the majority of August, September had an active start with a cool down on the 5-6th, a brief weekend warm up on the 7-8th, and another strong cool down this morning that sent low temperatures down to 40 degrees in Sussex, NJ. The pattern extremes only increase this week, varying between mid July-like heat and October-like temperatures only within a few days. Posted to the left are the initialized 850 millibar temperatures in Celsius and geopotential heights from the 18z NAM run (Image credit: NCEP Models), representing the 2 PM conditions from earlier today. A strong warm air mass can be seen over Iowa, with 850mb temperatures near 24-27C, supporting widespread surface temperatures in the 90s. A relatively strong westerly flow aloft will quickly push this warm air mass to the east, leaving it with little time to moderate before entering the region on Tuesday, when strong warm air advection will take place and the surface warm front moves through. 850mb temperatures of 20-22C are expected to spread into the Northeast between Tuesday afternoon and Wednesday evening, making it the 2nd warmest air mass of this year, behind the mid July heat wave. Meanwhile, southwest winds at the surface will advect a much more humid air mass into the region from the Southeast US, bringing dew points into the low to mid 70s. This combination of a warm air mass, humid conditions, and partial sunshine will make Wednesday unusually hot for this time of the year with near record temperatures for some.


18z 4k NAM forecast high temperatures for Friday (Image credit: PSU e-Wall)

temp48Forecast for NYC area: The heat will begin to be felt on Tuesday as the warm front quickly moves through in the morning hours, with overnight lows steady from the upper 50s inland to the mid 60s near NYC. The strongest forcing will remain well north of the area, although isolated showers are possible tonight with mostly cloudy skies. Clearing skies are expected by the late morning hours on Tuesday with mostly sunny and much warmer and humid conditions for the afternoon and evening, with highs peaking in the mid to upper 80s from NYC and north/west, and ranging from the upper 70s in eastern LI/CT to the mid 80s in western LI/CT. Highs near 90 in northern NJ are not out of the question. After a mild night with lows struggling to fall below the upper 60s to low 70s, partly sunny skies are expected on Wednesday with a SW wind at 5-10 mph and highs reaching the low to mid 90s away from the coast, where highs in the mid-upper 80s are expected. With the humid conditions, heat index values are expected to reach the upper 90s in the immediate NYC area, and may reach and/or exceed 100 degrees in NE NJ and NYC. While temperatures will fall short of record highs in NYC and NE NJ set in 1983 when highs reached 99 degrees, temperatures are likely to approach and/or reach record highs in Islip (88 degrees, 1989), Bridgeport, CT (90 degrees, 1983), and LaGuardia (96 degrees, 1983).

Warm overnight lows are expected again on Wednesday night, only falling into the low to mid 70s, but with a cold front approaching the area on Thursday producing widespread cloud cover and thunderstorms, possibly strong to locally severe. Widespread cloud cover will limit high temperatures into the low 80s inland and the mid to upper 80s for the rest of the area, with highs peaking early in the day before more widespread clouds and storms move in. The highest risk of storms is likely towards northwestern areas, where storms could be strong with heavy rainfall and strong wind gusts, with storms continuing through the late evening hours as the cold front moves through, pushing the warm air mass offshore.


Friday – Weekend: October-Like Temperatures

The region will turn from one extreme to another in only 1-2 days, as behind the cold front on Thursday night, an unseasonably cool air mass will dig into the region, with strong cold air advection bringing October-like temperatures for Friday and the weekend. Partly sunny skies are expected with a NW wind and highs peaking in the upper 60s-low 70s inland and the mid 70s for the rest of the area, with slight changes possible to the temperature outlook. Breezy NW winds will continue overnight with partly cloudy skies and lows falling into the low-mid 40s inland, low-mid 50s in NYC, and the upper 40s-low 50s elsewhere.

There is some uncertainty on Saturday regarding a possible upper level low that may cut off over the region as the ECM indicates, or continue moving east according to the GFS. At this time, I placed western parts of the area with mostly sunny skies and eastern areas with partly cloudy skies, although this aspect of the forecast may change around a bit. Unseasonably chilly high temperatures are expected, peaking in the low-mid 60s inland and the mid to upper 60s for the rest of the area; should the ECM scenario verify with a slower upper level trough cutting off over the region, temperatures may be even cooler. Chilly temperatures are expected overnight, falling into the 40s across the area except for NYC in the low 50s, with upper 30s possible inland. Frost is possible, if not likely to the north and NW of the area. Mainly sunny skies are expected on Saturday with highs warming back into the upper 60s inland and the low-mid 70s for the rest of the area.


Next Week: Mid Week Cool Down Possible

With the high pressure sliding east of the area, warmer temperatures will return for next Monday, with highs back well into the 70s. By that point, the models significantly diverge, ranging from the GFS bringing another significant cool down with well below average temperatures, to the CMC keeping seasonable temperatures, to the ECM depicting a significant late week warm up. The uncertainty lies in the pattern aloft, with the ECM keeping a Canadian shortwave weak and progressive, which along with aggressively pushing troughing east into western Canada, leads to rising heights in eastern North America. The GFS, however, is not nearly as progressive with the northeast Pacific troughing, and depicts a stronger and more amplified Canadian shortwave which digs southeast into the region, bringing another round of chilly temperatures. While this is too far away to make a high confidence outlook, at this time preliminary thinking is for cooler air to affect parts of the region, with warmer temperatures occasionally spreading into the region beyond 9/18 but without becoming sustained. Stay tuned for more information on the longer range.

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