Aug 23, 2012: Mostly Dry, Seasonable

Forecast Highlights:

– Generally seasonable temperatures to continue
– Some showers possible for early week

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Thursday, August 23 Observations:

Temperatures slightly warmed up on Thursday as mostly sunny skies returned with a high pressure moving into the region. High temperatures were warmer than those of Wednesday, reaching the mid to upper 80s from NYC and further north/west and the upper 70s to mid 80s across Long Island and southern CT. The highest temperature was 88 degrees in Caldwell, NJ, with the coolest high 78 degrees in New London, CT.

Forecast Overview:

The forecast through mid next week remains unchanged; mostly sunny skies with highs in the low to mid 80s east of NYC and mid to upper 80s NYC and N/W are still expected for Friday. Partly cloudy skies are expected from Saturday through Monday along with the risk of isolated showers, with highs cooling down into the upper 70s to lower 80s across most of the area, perhaps a bit cooler further east in Long Island. A cold front will move through the region on Monday night and Tuesday, resulting in scattered showers and storms with highs on Tuesday slightly warmer, followed by a trough moving into the region on Wednesday with highs cooling back down a bit into the upper 70s to lower 80s for most of the area. The longer range becomes more uncertain due to significant differences regarding what Isaac’s remnants will do once over the US, resulting in significantly lower confidence in the forecast at this time beyond the middle of next week.

Tropical Storm Isaac: Will Not Move Up The East Coast

Over the last few days, there has been speculation regarding the possibility that Tropical Storm Isaac moves up the East Coast, similarly to last year’s Irene. As my expectations have been with the previous two updates and are still mostly unchanged other than increased confidence and minor track/intensity adjustments, Isaac will not move up the East Coast, instead heading into the eastern Gulf of Mexico region.

Isaac’s Intensity: As expected from last night, Isaac continues to struggle with its organization and thus has failed to intensify much, with sustained winds at 45 mph and a minimum pressure at 1001 mb. Although Isaac’s center is not far SE of Haiti, the majority of its convection remains displaced to the southwest of the center. Isaac has less than 24 hours left before it makes landfall in Haiti on Friday, and given its current issues, will not strengthen much prior to landfall; I am expecting Isaac to make landfall with sustained winds between 45-50 mph. Following landfall, Isaac is expected to stop strengthening and at least slightly weakening due to land interaction.

The intensity forecast becomes more complicated as even a slight change in the forecast track will have an impact on Isaac’s intensity. At this time, Isaac is expected to move over Cuba near its northeastern coast; should Isaac remain entirely over Cuba before exiting to the NW, it will end up weaker, and will struggle to intensify again right after coming offshore. Should Isaac end up less over Cuba and more over water, however, it may not weaken as much, and would end up stronger going into the Gulf of Mexico. At this time, my forecast track keeps Isaac in the northeastern coast of Cuba as a 45 mph storm, although some minor changes are still possible. Isaac’s intensity in the Gulf of Mexico is more uncertain, although intensification to hurricane intensity is expected should Isaac easily survive its passage through Hispaniola and Cuba.

Isaac’s Track: After briefly moving WSW last night, Isaac turned to the WNW today, although it will still end up mostly south of Hispaniola before making landfall in the westernmost parts of Haiti. Isaac will then continue WNW towards Cuba; there is still some uncertainty regarding whether Isaac spends more time over Cuba or over water, which as previously mentioned will also determine its intensity. Isaac will continue to be steered to the WNW/NW, and while there is a weakness in the ridge to its north, Isaac will not turn north and move up the coast, especially with ridging slightly rebuilding to its north; there is no model support for such a solution, and such a track is not expected. Model solutions range from the NAM, which was the northeastern outlier today taking Isaac east of Florida, to the ECM, the western outlier taking Isaac into western Louisiana. Although the ECM did correctly start the trend of Isaac moving through the Gulf of Mexico as opposed to the eastern coast of Florida, it still appears to be a bit too far south/west, and at this time I am siding with a solution in between, a bit closer to the GFS, with landfall possible somewhere around far western Florida. The exact location of the landfall is still subject to change within that general region, however.

Isaac’s Impact on the US: Although Isaac will not move up the East Coast, its remnants will affect parts of the central/eastern. There is still uncertainty with exactly where Isaac’s remnants will end up tracking once Isaac tracks inland, although the potential is there that the remnants may affect at least parts of the Mid Atlantic and Northeast region. More information will be posted regarding Isaac’s inland impact in the US once confidence increases regarding the location of Isaac’s landfall.

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