Oct 22, 2012: Watching Early Next Week

10/23 Morning Update: A poll has been added in the right side of the blog about the possibilities for the storm. Stay tuned for brief updates in the NYC Area Weather Twitter page before the evening discussion.

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Forecast Highlights:

• Some showers Tues, Weds; cooler temps
• Moderate warm up for weekend; highs back in 70s
• Uncertainty with cold front and Tropical Storm Sandy interaction for early next week

The model guidance remains split today regarding a storm early next week, with some showing a significant storm affecting the region while others show nothing of interest. Click below to read the full post for more information on this time period.

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Tonight - Thursday: Cooler, Some Rain

Temperatures today ended up warmer than expected, peaking in the mid 60s to low 70s from NYC and further north/west and the mid 60s for most of Long Island and southern Connecticut. Despite the warmer temperatures today, however, scattered showers and a back door cold front will lead to slightly cooler temperatures going into the middle of the week. Moderately warm temperatures are expected again tomorrow with highs in the mid to upper 60s for most of the area, although if the actual temperatures are different than the forecast, they would likely be cooler than currently expected. Scattered showers are expected again on Tuesday night, with mostly cloudy skies on Wednesday and highs in the mid to upper 60s from NYC and further north/west and the low to possibly mid 60s in Long Island and southern CT. As with Tuesday, the forecast highs on Wednesday are somewhat uncertain and subject to some changes. A slight warm up in temperatures is expected for Thursday with drier conditions and more sunshine.


Friday - Longer Range: Watching Storm Potential

Ridging will build back into the area on Friday into the weekend as more of a SSW flow develops, with temperatures surging again well into the 60s across the area and the low 70s for the immediate NYC area, although cooler temperatures are likely for Long Island and southern Connecticut, likely in the mid 60s but subject to some changes.

The highlight of the medium range forecast remains a potential significant storm for the region showing up on some of the model guidance for early next week, showing Tropical Storm Sandy phasing and retrograding into the Northeast as an abnormally strong hybrid/extratropical low. The most bullish models today were once again the ECM and CMC, showing a storm of historic magnitude affecting the region with extreme winds, heavy rain, and even snow. The 12z CMC, posted to the left (image from Pennsylvania State University e-Wall), shows a major storm slamming into New Jersey; the ECMWF handles the timing and location differently, but also shows a major storm for the Northeast. Such a solution, if it were to verify, would result in a damaging storm along the majority of the Northeastern U.S. Other models, however, are showing a significantly different outcome, led by the GFS which takes the storm well offshore with no impact on the region.

It is important to note that the storm is still 7-9 days out, which can make a huge difference between the current forecasts and the actual outcome. As such, it is still too early to make a high confidence call regarding either solution. As discussed below, there are still several key factors that need to perfectly come together for such a high impact event to verify.

Tropical Storm Sandy: Invest 99L in the Caribbean has continued to become better organized, and has intensified into a tropical storm today, receiving the name "Sandy". Sandy is currently a 45 mph tropical storm with a minimum pressure of 998 millibars, and is stationary in the Caribbean sea south of Jamaica. Sandy is expected to begin tracking to the NNE tonight while quickly intensifying, perhaps rapidly, reaching Jamaica and Cuba on Wednesday and Thursday. By landfall, Sandy should be a category 1 hurricane, and in the case rapid intensification takes place, upper-end category 1 intensity (85-90 mph) may be within reach and Sandy would reach category 1 intensity earlier than currently forecast (Tuesday evening-Weds morning). Afterwards, Sandy will move into the Bahamas, where the uncertainty begins.

One factor that will affect the future of Sandy is a strong low in the North Atlantic. For the short range, a strong block will build east of Greenland, along with a trough near Newfoundland and ridging over the eastern US. As the block and the eastern US ridging connect, the trough will split with a closed 500 millibar low developing southeast of Newfoundland, around the same time that Sandy moves into the Bahamas. One of the uncertainties at this time is regarding the non-tropical low. Most of yesterday's models blocked Sandy from moving east and well offshore. With today's runs, the GFS quickly takes Sandy ENE from the Bahamas, in contrast to the ECM and CMC which take it northeast closer to the East. This part of the forecast also depends on how far west or east Sandy ends up as well; a further east track would be less favorable for a direct East Coast impact, while a further west track wouldn't guarantee direct impact but would at least increase the probability.


U.S. Pattern: The other key factor in addition to Sandy is the shortwave(s) responsible for the potential storm. The first shortwave has its origins in the Gulf of Alaska, a region with poor sampling of data which makes it more difficult for the model guidance to accurately forecast the final outcome. Until it moves onshore into the western US on Wednesday night, when it will have more sampling, the model guidance is expected to continue having difficulties handling the specific scenario regarding any phasing with Sandy.

The biggest trend with today's model guidance, however, has been for the models that do phase Sandy to do so with a different shortwave behind the initial one, which simply moves into Canada. Both the ECM and the CMC show another shortwave entering the NW US on Friday, behind the initial one, which then phases with Sandy and results in the significant storm. The GFS, in addition to showing Sandy further east, has Sandy missing the first shortwave, with the second shortwave staying well to its northwest as Sandy continues to move northeast, far away from the US. Even if the 2nd shortwave is favorable for phasing, Sandy's location also comes into question; as the latest 0z GFS run demonstrated, even if the shortwave is more amplified and reaches the Northeast, full phasing would not happen if Sandy is too far east in the Atlantic. Although the latest guidance shows phasing with the 2nd shortwave, considering that there will continue to be differences with the model solutions for the next few days, the possibility remains that Sandy phases with the first shortwave or with none of them.


Summary: There is still plenty of uncertainty regarding this time frame, and additional changes are expected in the model guidance over the next few days until the energy from the Pacific is sampled, which will take a few days. There is not enough confidence to go with any high confidence calls, although at this time the GFS far eastern solutions appear to be potential outliers, along with the extreme CMC and ECM solutions at least regarding intensity, which show an extremely intense sub-940 millibar low pressure affecting the region. At this time, the only solid conclusion that can be drawn is that the potential is clearly there for a moderate to possibly significant storm to affect the region, but the timing, impacts and the exact scenario remain uncertain. Most solutions remain on the table, ranging from a significant impact storm containing heavy rain, strong winds and possibly interior snow, to a storm mostly offshore with some rain. At this time, I am leaning towards a moderate impact storm, although this is still subject to change. Stay tuned for more information on this storm potential over the next few days.