Sept 8, 2013: 90 Degrees May Return Wednesday

Forecast Highlights:

heatA cold front currently moving through the region will bring another seasonable day, with chilly temperatures returning for tonight and Monday with clearing skies and decreasing winds. Even though it’s almost the middle of September, summer-like heat and humidity will return for Wednesday, with temperatures in the upper 80s-low 90s away from the coast, which combined with humidity will lead to heat index values in the mid 90s. This heat will be short lasting, however, with much cooler temperatures returning for next weekend, followed by a warmer pattern returning for next week.


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Saturday, September 7 Observations:

9.7.13Chilly temperatures were observed again on Saturday morning, but with a warm air mass quickly returning into the region, bringing mostly to partly sunny skies, a southwest wind, and highs in the mid to upper 70s across the area, peaking at 80 degrees near NYC. Showers ahead of an approaching cold front approached the area from the north in the evening, but mostly dissipated with only isolated showers in northern areas. The warmest temperature was 80 degrees in Teterboro and Newark in NJ and Central Park, and the coolest high temperature was 73 degrees in Montauk, NY and Westhampton Beach, NY.



Today – Monday: Dry, Chilly Again

The next two days continue this month’s theme of frequent fluctuations in temperatures, following Friday’s cool down and yesterday’s warm up. A cold front is currently moving through the region, with isolated showers or thunderstorms possible before the early afternoon hours, followed by clearing skies, a breezy NW wind at 10-15 mph, and highs peaking in the low to mid 70s inland and the mid to upper 70s for the rest of the area, likely reaching 80 degrees near and/or southwest of NYC. Clearing skies and decreasing winds are expected tonight with lows ranging from the low 40s inland, mid 40s to near 50 degrees in the north/west suburbs and southern CT, upper 40s-low 50s in long Island away from the coast, and low-mid 50s in NYC and the coast. Mostly sunny skies are expected on Monday with highs in the upper 60s to low 70s inland and the low to mid 70s for the rest of the area.


Tuesday – Thursday: Hot, Humid Conditions Briefly Return

heatHeat and humidity will make a brief yet strong comeback across the region as an unseasonably warm air mass surges into the region. A cold front will move through early on Tuesday; while this front appears to be lacking enough moisture to produce widespread precipitation, isolated thunderstorms can’t be ruled out north of NYC. Behind this warm front, a much warmer and more humid air mass will spread into the region, with 850mb temperatures near 18-20C, among the warmest of the whole summer, and dew points in the upper 60s to low 70s. This will begin to become more noticeable towards Tuesday in the late afternoon, with highs reaching the low to mid 80s from NYC and further north/west and the mid 70s-low 80s further east.

The hottest temperatures are expected on Wednesday, with mostly to partly sunny skies, wind from the southwest at 5-10 mph, and highs peaking in the upper 80s away from the coast with low 90s possible in northeast NJ. Along with humid conditions, heat index values are expected to reach the low to mid 90s. Overnight lows will remain mild, struggling to fall below the mid-upper 60s inland and the low-mid 70s near NYC and the coast. A cold front will move through the area on Thursday, pushing the hot and humid air mass out; scattered thunderstorms are expected across the area, possibly heavy and/or strong, with slightly cooler high temperatures reaching the low to mid 80s.


Friday – Weekend: Chilly Temperatures Expected

A significant contrast in temperatures is expected between the mid week heat and the weekend, when a much stronger cool air mass enters the region behind Thursday’s cold front. Partly sunny skies and breezy NW winds are expected to return towards Friday with highs likely cooling down into the low-mid 70s inland and the mid-upper 70s elsewhere, with noticeably lower humidity. The main uncertainty at this time is regarding the setup of the trough and how slow the cold front is to depart, with the GFS the more progressive model quickly bringing the trough into the region, resulting in unseasonably cool temperatures, while the ECM is slower, developing a cutoff low pressure over New England which keeps daytime highs chilly but with much warmer overnight lows than the GFS, which would support widespread 30s inland. At this time, I am siding towards slower timing of the trough than the GFS; while there is uncertainty regarding the potential cutoff low, this scenario will continue to be watched, which would result in more cloud cover and warmer overnight lows than currently forecast should it verify.

Daytime highs are likely to be the coolest on Saturday, with highs only in the mid-upper 60s across most of the area forecast at this time. Overnight lows depend on any potential cutoff low; should the front continue to push offshore with the high pressure building in, chilly overnight lows would take place on Saturday night with widespread 40s, possibly near/slightly below 50 degrees in NYC, and mid-upper 30s inland. At this time, I went with slightly warmer temperatures in the 7-day forecast accounting for potential slower timing of the front, with the temperature outlook subject to change. Cooler than average temperatures are likely to continue through Sunday and Monday with mostly clear skies as a high pressure builds into the region.


Next Week: Warmer Temperatures Return Again

temp_anomaliesThe up and down temperature trends of September continues beyond the weekend, with another warm up expected. With the polar vortex settling over Greenland and the northern Davis Strait, continuing the +NAO pattern that has been in place since August, and a trend for lowering heights aloft in western North America, ridging will shift east to focus on the eastern half of the US, especially over the central US with above to well above average temperatures likely in the Midwest, Great Lakes and southern Canada. The impact this pattern has on the area depends on several factors, including whether a cutoff low forms or not from the weekend trough over New England and/or Atlantic Canada, and the strength and amplitude of several shortwaves crossing through Canada and/or the Midwest. The more progressive scenario would keep the weekend trough moving offshore and the Canadian shortwaves weaker and well to the north, resulting in a widespread ridge covering the area with sustained above average temperatures, back into the 80s. The slower scenario, with either a cutoff low northeast of the area or a stronger and further south Canadian shortwave, would keep the region in the eastern end of the ridging and more vulnerable to back door cold fronts, with one possible on 9/17. The warmth would still reach the region after at least 9/18, but in a delayed and shortened form.

An experimental week 2 temperature outlook has been posted above. Confidence is medium, with areas of uncertainty regarding how far south above average temperatures extend in the Mid Atlantic and how far west in the central US, and the southern extent of cool anomalies in the northwest US. More specific details on the longer range outlook will be posted as this time frame gets closer.

2 thoughts on “Sept 8, 2013: 90 Degrees May Return Wednesday

  1. Anonymous Reply

    Any showers/thunderstorms expected in NYC and Long Island before the cold front passes through?

    • NYC Area Weather Post authorReply

      The front is currently moving through the area; although an isolated shower can’t be ruled out, dry conditions will mostly persist until Thursday.

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