Aug 22, 2012: Dry Conditions Through Monday

Forecast Highlights:

– Partly sunny, little rain through weekend
– Storms may be possible early-mid next week


Wednesday, August 22 Observations:

Mostly dry conditions were observed across the area on Wednesday, although a heavy thunderstorm popped up over NE Essex county during the afternoon, resulting in localized flash flooding with above 2 inches of rain in that small area. Temperatures were generally similar to those of Tuesday with highs in the lower 80s for most of Long Island/S CT and the lowre to mid 80s from NYC and further north/west. The highest temperature observed was 89 degrees in Teterboro although as observed several times earlier in the month, its high is noticeably higher than surrounding stations between 82-84 degrees.

Forecast Overview: More Clouds/Few Showers For Weekend

Little changes in the set up are expected through Sunday and possibly Monday with a high pressure over the region, focusing north of the area, with mostly to partly cloudy skies expected. Highs will be slightly warmer for Thursday and Friday, reaching the lower to mid 80s from NYC and further north/west, exceeding 85 degrees in the immediate NYC area, with upper 70s to lower 80s in most of Long Island/S CT.

Showers and clouds will stall offshore in the late week, and could advance north into parts of the area especially further south/east later on Saturday into Monday. Highs are likely to end up in the mid 70s to lower 80s across the area with partly to perhaps mostly cloudy skies along with a risk of isolated showers, especially east of NYC. The next cold front will then approach the area on Monday and Tuesday with a risk of showers and thunderstorms with highs likely remaining similar to those of the weekend. Behind the front, there is more uncertainty depending on exactly what Isaac does, although temperatures may remain in the upper 70s to lower 80s range.

Tropical Storm Isaac: More Likely To Enter Gulf of Mexico

Until yesterday, Isaac had many similarities to last year’s Irene; both were each season’s 9th named storm starting with an “I”, both formed in the same region, one day apart, and they were generally moving in the same direction. As yesterday’s update mentioned and is still expected as of today, however, despite the similar beginning, both storms will not have the same ending. Irene went on to move up the East Coast and produce widespread flooding and damage, while Isaac is taking a route towards Florida and perhaps the northeastern Gulf of Mexico.

Isaac’s Intensity: Isaac, as with other storms in this basin earlier this year, has failed to significantly intensify. Isaac continues to quickly move west, with its forward speed having varied between 18-22 mph today. Dry air is still having some impact on Isaac, and despite its large size, it remained disorganized without a well defined center throughout the day and held at 45 mph as of NHC’s 11 PM update. Since then, stronger convection has been forming on top of Isaac, although it’s not completely consolidated yet, with the latest satellite loop showing the convection pushing to the SSW. With Isaac approaching the mountains of Hispaniola, known for disrupting tropical cyclones, Isaac has a small window of opportunity to organize itself and intensify into a hurricane. With the limitations ahead of Isaac, I am expecting gradual intensification into a strong tropical storm prior to reaching Haiti, with a weak category 1 hurricane not out of the question should Isaac be able to organize itself tonight and intensify faster on Thursday.

There is uncertainty regarding whether Isaac moves over Hispaniola or stays to the south; the latest model guidance takes it over the island, although the trend has been slightly to the west, and especially if the latest satellite observations prove to be a SW wobble in Isaac’s track, it may help Isaac to either stay near the southern edge of Hispaniola or barely miss the island to the south. Isaac is then expected to track over Cuba; both of these islands will likely disrupt Isaac to some extent, preventing Isaac from becoming a stronger hurricane in the Caribbean basin. Once it emerges from Cuba, latest trends point to Isaac staying west of Florida; should this be the case, which is increasingly likely as will be discussed below, additional intensification is expected in the eastern Gulf of Mexico, which is where Isaac will have a better chance of intensifying into a stronger hurricane. The exact track is still uncertain, although it is recommended that the entire Gulf of Mexico coast from Louisiana to Florida pay close attention to Isaac.

Isaac’s Track: As discussed yesterday, there are already differences with Isaac and Irene which continued to grow today; Irene went over Puerto Rico and north of Hispaniola while becoming a strong Category 1 hurricane; Isaac, however, is staying south of Puerto Rico and will approach the southern coast of Hispaniola as a strong tropical storm or weak hurricane. Especially if the latest satellite trends are an indication of a SW wobble in Isaac’s track, it may keep Isaac slightly south of the latest model consensus, which further decreases the probability of Isaac moving up the East Coast. A weakness in the ridge north of Isaac is expected as it approaches Cuba, with Isaac turning more to the NW, although especially with its continued west track, it is an increasing likelihood that Isaac enters the eastern Gulf of Mexico. A forecast track map will be posted with Thursday night’s update; at this time, I would place the cone of uncertainty from eastern Florida to New Orleans, with the main track going into NW Florida.

Impact in the rest of the US: Once Isaac makes landfall in the US, which is likely, its remnants would make their way north, which could spread heavy rains associated with Isaac further inland. The location of where this happens is still uncertain, however, and depends on where Isaac makes landfall and the direction in which it will be moving. The possibility is there that Isaac’s remnants may reach the region, although Isaac is not expected to be a tropical cyclone should it affect the region. Stay tuned for more information on Isaac’s impact in the US.

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