Aug 25, 2012: Isolated Storms Through Tuesday

Forecast Highlights:

– Isolated storms continue Sun, scattered storms Mon-Tues
– Briefly cooler temperatures for Weds-Thu; 50s for lows
– Gradual warm up for late next week

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Saturday, August 25 Observations:

Following Friday’s warm temperatures, cooler temperatures were observed on Saturday with more cloud cover and isolated storms over northern NJ during the mid-late afternoon hours. Temperatures ended up in the lower to mid 80s in the immediate NYC area and the upper 70s to lower 80s in Long Island/S CT. The estimated temperature outlines were not filled in for western NJ due to missing data from the three NWS observing stations in that region. Remarkably, Central Park had the warmest high temperature in the area, tied with Teterboro; this is the first time this has happened this summer.

Tonight – Tuesday: Clouds, Scattered Storms

Partly to mostly cloudy skies will continue over the next few days as clouds and storms drift north from the southern Mid Atlantic. Most storms will stay west and southwest of the area, towards Pennsylvania, although mostly cloudy skies and isolated storms are still expected for Sunday with highs in the lower to mid 80s from NYC and further north/west and the upper 70s to lower 80s in Long Island/S CT. A cold front will then approach the region on Monday, moving through the area on Tuesday. Mostly cloudy skies will continue on Monday and at least parts of Tuesday with scattered storms expected especially for Monday night and Tuesday. High temperatures on Monday will be similar to those of Sunday, if not slightly cooler, with slightly warmer temperatures for Tuesday.

Wednesday – Next Weekend: Cool, Warmer, Then Rain Possible

A trough will briefly move into the region for Wednesday and Thursday, resulting in colder temperatures as a high pressure moves in with 850mb temperatures dropping to near 10C. Wednesday is expected to have highs in the upper 70s to lower 80s across most of the area, with slightly warmer temperatures for Thursday, although overnight lows on Wednesday are expected to be quite cool; with mostly clear skies and a cool air mass, low temperatures are expected to drop into the 50s away from NYC, with low 50s inland towards NW NJ/SE NY. It is not out of the question that a few interior areas may drop below 50 degrees, although for now I am sticking with low 50s in the 5-Day Forecast.

Temperatures will then gradually warm up for the late week as warmer 850mb temperatures move into the region, with widespread low-mid 80s for highs returning on Friday, possibly a bit warmer in the immediate NYC area. The question then becomes what happens with Isaac’s remnants, as there are two main possibilities at this time; one is where Isaac slows down after landfall in the Gulf of Mexico and is pushed east towards the Southeast coast and then offshore, the other is where Isaac continues to drift north into the central US, with its remnants then moving further east/northeast into the Northeast and/or Mid Atlantic, possibly including the NYC area. Until the exact scenario for Isaac once it moves inland becomes clearer, confidence remains lower for next weekend’s outlook, although the possibility is there for storms to affect parts of the region, possibly including the area, perhaps associated with Isaac’s remnants. Stay tuned for more information on next weekend’s outlook.

Tropical Storm Isaac: Approaching Florida
**Updated at 10 PM to add new information and map

Following Isaac’s sudden late minute intensification burst last night, Isaac made landfall in the western tip of Haiti, which disrupted Isaac’s developing inner core and caused the storm to weaken from a 70 mph tropical storm to a 60 mph tropical storm with a minimum pressure of 1000 mb this afternoon. Since then, however, Isaac’s minimum pressure has slightly dropped to 997 mb as Isaac managed to avoid spending a prolonged period of time over central Cuba.

Isaac’s Track: Isaac is currently just north of the coast of eastern to central Cuba, and is moving NW. A general NW motion will continue for the next 2 days as weak ridging rebuilds north of Isaac with the tropical storm expected to move through the Florida keys late on Sunday through early Monday. This path will then take Isaac into the Gulf of Mexico, where it will continue to move WNW/NW before gradually turning more to the north later in the period as it approaches the Gulf coast. The model guidance differs regarding where landfall takes place, with the GFS showing landfall around the New Orleans region and the ECMWF showing landfall southwest of Tallahassee, FL; with Isaac’s current fast speed and the continued WNW/NW steering currents, as well as recent trends with the model guidance to shift the landfall west, my adjusted forecast has Isaac making landfall in southeastern Mississippi, although the exact location is still subject to change and may end up somewhere between central Louisiana and southwest of Tallahassee, FL.

Isaac’s Intensity: Land interaction has taken a toll on Isaac today as its appearance has become less organized during the day following Isaac’s Hispaniola and Cuba landfalls. Isaac has slightly strengthened over the last few hours with the minimum pressure dropping 3 mb, although the latest observations as of 10 PM show that more convection is forming near Isaac’s center northeast of Cuba. While the environmental conditions are not completely supportive for rapid intensification with the lowest wind shear still southeast of Isaac’s center and Isaac still not showing a very organized appearance, additional intensification is likely to take place overnight into Sunday, and it is not out of the question that Isaac becomes a hurricane a bit earlier than currently forecast.

Once Isaac moves into the Gulf of Mexico, however, conditions will be much more favorable for intensification, and the possibility is there that Isaac may rapidly intensify in that region depending on how it emerges into the GOM. At this time, Isaac is expected to reach category 2 intensity, and should rapid intensification take place, category 3 hurricane could very well be within reach. Most of the models at this time strengthen Isaac into a strong category 1 hurricane; I am going more bullish than the model guidance with the intensity given the rapid intensification potential, but a little conservative compared to Isaac’s full potential, stronger than a weak-moderate category 3 hurricane, although this will only be possible should Isaac end up with near ideal conditions for rapid intensification which is not a high confidence call at this time. The possibility is there that Isaac may fail to quickly intensify, in which case it would not intensify much more than strong Cat 1/weak Cat 2 intensity and my forecast intensity may have to be adjusted slightly downwards, although environmental conditions in the Gulf of Mexico appear supportive of more intensification, potentially rapid. The current intensity forecast is not final yet, however, and may still be revised downwards or upwards.

Regardless of exactly where Isaac makes landfall and with what intensity, Isaac has the potential to be a damaging hurricane where it makes landfall, and the entire Gulf coast from western Louisiana to Tallahassee, FL, including New Orleans, needs to keep a close eye on Isaac with a hurricane landfall likely.

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