Sept 18, 2013: Warmer Temps Return By Late Week

Forecast Highlights:

f138A cold air mass remains in place this morning with chilly October-like temperatures, as low as 34 degrees in Westhampton Beach, NY. The trough will gradually begin to move out with temperatures moderating into the mid-upper 70s by the late week, followed by a frontal passage around Sunday. The tropics may have to be watched afterwards as a storm with tropical connections may affect parts of the eastern US.


<< September 16 | September 17 | September 18 >>

Tuesday, September 17 Observations:

9.17.13Behind the cold front, much cooler temperatures returned into the area, ending up at least 10 degrees below average. Morning temperatures reached 50 degrees in Central Park, making Tuesday the coolest mid September morning since 9/16/2007. Mainly sunny skies were observed during the day with highs only peaking in the low to mid 60s across the area. The highest temperature was 68 degrees in Somerset, NJ, and the coolest high temperature was 62 degrees in Shirley, NY and Westhampton Beach, NY.



Today – Friday: Warming Up

As previously mentioned, temperatures were unseasonably cold this morning, falling as low as 39 degrees in Sussex, NJ; 37 degrees in Danbury, CT; and even 34 degrees in Westhampton Beach, NY in the Pine Barrens of Long Island. A strong high pressure was present overhead, providing the area with clear skies and calm winds, an ideal setup for strong radiational cooling allowing for locations outside of the immediate NYC area to significantly cool down. Central Park failed to cool down as much, and is currently at 51 degrees as of 7 AM, but this still marks the second consecutive morning of such temperatures and the coolest mid-September morning since 2007.

The high pressure will remain overhead today, bringing another day of mainly sunny skies with highs reaching the upper 60s to low 70s across the area. Clear skies are expected again tonight with strong radiational cooling again resulting in chilly overnight lows, but with the air mass not as cold as this morning; lows are expected to fall into the low-mid 40s in NW NJ, Orange County in NY, interior CT and the Pine Barrens of Long Island, mid-upper 40s in the north/west suburbs of NYC, southern CT and the rest of Long Island, and the low-mid 50s in NYC and the immediate coast. The warming trend will continue for the late week with mostly sunny skies and a southwest wind, as highs on Thursday rise into the low-mid 70s inland and near the coast and the mid 70s elsewhere, and on Friday into the low-mid 70s near the coast and the mid-upper 70s elsewhere.


Weekend – Next Week: Some Rain/Storms, Watching The Tropics

A low pressure will develop near the Midwest US on Wednesday, tracking northeast as it intensifies into a strong mid-latitude cyclone over central Canada by Friday and Saturday, dragging a cold front to the east through the Ohio Valley and eventually the northeast US region. As the low pressure remains well to the north and closes off by Saturday, the strongest forcing will lift to the north as well, and the front will weaken and slow down as it approaches the region. Partly cloudy skies are expected on Saturday with highs in the mid to possibly upper 70s, with scattered thunderstorms spreading into the area overnight and into Sunday with mostly cloudy skies.

f138The pattern becomes more complex by early next week as the tropics may get involved. Barely days after hurricane Ingrid made landfall in Mexico, producing additional flooding in a region that has been hit with multiple tropical cyclones this year, another tropical disturbance labeled 95L is currently entering the Gulf of Mexico, and is expected to become a tropical storm in that region, which should it do so, it would be named Jerry, the 10th named storm of the 2013 Atlantic hurricane season. When Ingrid was present, a strong mid level ridge to its north kept it on a westerly path. In this case, however, several pieces of energy will become involved, associated with the remnants of Ingrid as vorticity moves north from Mexico, then east into the southern US, where it is expected to interact with energy splitting from the late week trough associated with the Midwest low pressure. This combination will lead to lower heights aloft in the southern US gulf coast, which if Invest 95L intensifies and stays as north as currently forecast, would pull 95L north towards the US gulf coast, where it would lose tropical characteristics and develop into a coastal low pressure producing widespread heavy rainfall in the southeast US. As the central Canada storm moves out and strong troughing amplifies over the western US, the jet stream will likely rise north of the region, allowing the potential southeast US system to track NE towards the region.

The latest 6z GFS run has been posted above (image credit: PSU e-Wall), representing the potential storm over the southeast US with light rain extending north into the area. This far out, it is important to keep in mind the model guidance struggles handling the more specific aspects of the forecast, and the modeled track and intensity of the low are still going to change over the next few days. The model guidance varies with the track of this system, keeping the heaviest rains to the south of the area with either dry conditions or light rain in NYC, but this system will be watched for the possibility of a further north track and more rain over the NYC area. As with any medium range forecast, there are several scenarios that may result in this scenario failing to unfold, such as a weaker invest 95L and/or a different setup of the southern US troughing which would keep 95L in Mexico and the northeast US region under a high pressure with sunny skies and cool temperatures for the early week. Otherwise, temperatures are likely to end up below average again for the early week, gradually moderating back to above average with drier conditions by the late week. Stay tuned for more information on next week’s outlook.

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