Oct 25, 2012: Historic Storm Early Next Week

Brief Overview:

All attention is now focused on Hurricane Sandy, which is currently near the Bahamas and approaching the East Coast. While there remain some differences with the model guidance and uncertainties, probability is quickly increasing that the Northeast US may be on track to deal with a historic event. Click below to read the full post for an in-depth analysis of the upcoming situation and potential impacts.

---

Today - Saturday: While the highlight of the forecast is the significant storm on Sunday, there are still minor changes in the weather until the storm arrives. Temperatures will struggle to drop a lot tonight, and will rise into the mid 60s to low 70s on Friday with partly cloudy skies. Slightly cooler temperatures are expected on Saturday with mid to upper 60s as cloud cover increases.


Hurricane Sandy: A Potentially Historic Event

Slightly revised - 12 AM

The focus over the last few days has been on Hurricane Sandy and its potential impact in the Northeast. Over the last few days, the models have been inconsistent due to difficulty with handling the set up which resulted in differences, ranging from the ECMWF which had a historic storm affect the region to the GFS which harmlessly took the storm out to sea. Since then, however, model differences have decreased, and trends are pointing to a highly anomalous and potentially historic event affecting the region with impacts even more significant than last year's historic October snowstorm.

Expected Set-Up: As previously mentioned, this is a highly anomalous set up and is the result of several factors falling into place at the right time. The key player to this whole storm is Hurricane Sandy, which is discussed in more details in the next section. Sandy will continue to move parallel to the Southeast US coast in the short term. Typically, late October storms that originate in the Caribbean stay well offshore, but this will not be the case with Sandy due to an anomalous block near Greenland and Newfoundland and a cut off low pressure to its south, as ridging to the east of Sandy connecting to the northern block will prevent Sandy from escaping eastward and out to sea. Meanwhile, a strong trough will drop into the central and eastern United States, approaching the coast as it becomes negatively tilted. With Sandy blocked from moving further north and east, she will be captured by the trough and will sharply turn northwest, then west, retrograding into the Mid Atlantic region in an usual track for a tropical cyclone.

Track Forecast: By this point, it is nearly certain that Sandy will be captured by the trough and will retrograde into the Mid Atlantic and Northeast region. Until early today, the GFS model has been the outlier solution, showing Sandy staying much further east as it had weaker ridging to its east, which gave Sandy a small window to take a further east track, followed by showing a variety of odd solutions, at one point completely taking Sandy away from North America. My previous discussions mentioned how the GFS was a likely outlier solution, and with today's runs the GFS finally caught up to the rest of the model guidance, showing the capture and the retrograde into the US as well.

With the capture nearly certain, the question remaining is where it makes landfall. At this time, landfall cannot be ruled out for any location along the coast from southeastern Virginia to Cape Cod. Narrowing down the spread, considering minor location differences with Sandy and the trough prior to the phase as well as recent model trends, a reasonable range for landfall is between the central Delmarva Peninsula up towards NYC. The model guidance continues to trend south with the landfall location, led by the usually reliable ECMWF model which shows a further south landfall than the rest of the model guidance and even its ensemble mean. While the ECM may be a bit too far south, it may be onto the right idea with landfall in the Mid Atlantic as opposed to New England. The landfall location is still subject to change, although at this time my first call for landfall location is between central New Jersey and Delaware. Should current trends continue, future updates may make a sharper turn to the left with a further south landfall, although this is uncertain at this time. At the same rate, the possibility is there that the track may be adjusted further north towards central NJ or NYC, which could significantly increase the impact in the area.


Intensity Forecast: Last night, Sandy stopped just short of Category 3 intensity after rapidly intensifying prior to making landfall in Cuba. Sandy has since weakened into a category 2 hurricane, and is expected to further weaken to a category 1 hurricane over the next 2 days as it encounters higher shear to its north. Despite the category, however, Sandy is a large hurricane and will remain large in size. As it reaches the Northeast US and interacts with the trough, additional deepening is expected, with the minimum pressure likely to drop into at least the 940-950 millibar range, which is highly unusual for this region. By the time it makes landfall, a minor rise in the pressure is likely, although it will remain a very intense cyclone. At landfall, Sandy will not be a purely tropical cyclone nor an extratropical cyclone, but rather a hybrid cyclone with an asymmetric warm core, with both tropical and non-tropical characteristics.


The image below is from the 18z GFS as Sandy makes landfall in central New Jersey. Note the very tightly packed isobars, which reflect a very intense low pressure. Image from Penn State University e-Wall

Impacts in the Northeast: This is the most complicated part of the forecast. The specifics of the exact impacts for specific locations cannot be determined until the landfall location zone is narrowed down, although with a storm of this magnitude, significant impacts are expected across the region, which for many will overshadow the historic October snowstorm that happened a year ago, coincidentally on the same dates as this storm.

Wind: The storm will contain a very large wind radius, with strong wind gusts spreading across the majority of the Mid Atlantic and the Northeast, extending into parts of the Ohio Valley and Great Lakes regions as well. The strongest winds will be closer towards the landfall location with very tightly packed isobars, with gusts of 60 to 80 mph likely; in the worst case scenario, wind gusts above 80 mph may even be possible. Outside of the storm center, widespread strong wind gusts are expected as well, with the potential for gusts in the 40-60 mph range for many places away from the storm center. These wind gusts will easily be capable of producing widespread damage across the region, especially for coastal areas. Coastal flooding and significant storm surge will also be major issues regardless of where the storm makes landfall.

Rainfall: As with every large storm, precipitation will also have a large impact in the region. As this is a tropical cyclone becoming hybrid, tropical moisture will be pulled into the region, with widespread heavy rains expected west and south of Sandy's track. At this time, rain amounts in the region west and south of the storm, which are currently likely to be in the southern and central Mid Atlantic up to Pennsylvania and NJ, are likely to end up generally near 4 to 8 inches, with some locations seeing more than 8-10 inches of rain. North of the storm track in the Northeast US, less rain is expected, with at least 1 to 4 inches possible with locally higher amounts, although for interior location north of the low track the wind gusts are likely to be the main risk. This will be a prolonged rain event, as Sandy ends up stalling over the region, keeping cloudy skies and showers in place for almost a week, which will enhance the rain totals.

Snowfall: Hurricane Sandy is also expected to result in the potential for a significant wet snowstorm for western Pennsylvania, West Virginia, and portions of Virginia and North Carolina, landing on the same dates as last year's historic snowstorm. As Sandy will track from east to west, an unusual track for tropical cyclones, it will pull a warm air mass in its eastern side into the Northeast US while a strong cold air mass in its western side is pulled into its southern side. The most significant snowfall is currently likely in the mountains of West Virginia; heavy precipitation associated with the tropical moisture falling in the higher elevations with sub-freezing temperatures will result in the potential for significant wet snowfall, perhaps above 1 or 2 feet of snow. As the cold air will be in the south side of the storm, the potential is there for snow to mix in with the rain in areas that rarely experience snow in October, in the lower elevations of Virginia, although at this time this remains a potential and is not certain yet.


Potential Impacts in the NYC Area: At this time, given the uncertainty with the track and the exact landfall location, the exact impacts from Sandy regarding rain amounts and wind gusts are not set in stone and are subject to change. Based on my latest thinking that Sandy makes landfall between the northern Delmarva and central New Jersey, while the NYC area will be spared of the very worst in terms of wind and rain, there will still be significant impacts, especially along coastal areas with a significant storm surge and coastal flooding possible. The potential is there for at least 2 to 5 inches of rain, potentially higher should Sandy end up closer to the area than currently expected. Wind gusts are also not set in stone, although there is the potential for wind gusts to end up in the 40-60 mph range for most, with some areas above 60 mph. These are only preliminary figures and are subject to change, although this is to give an overall idea of the possible impact from Sandy. Should Sandy end up tracking near at least central NJ closer to the area, more significant impacts are expected, with more rain and stronger wind gusts reaching 60-80+ mph in the worst case scenario. By this weekend, there will be a better idea of the specific impacts in the area.


Summary: Hurricane Sandy is shaping up to be a potentially historic event for the Northeast US, as well as the biggest event of 2012 so far. While there is still uncertainty with the exact track of Sandy and the landfall location, Sandy is expected to result in significant impact across the region, with heavy rains resulting in flooding, damaging wind gusts resulting in downed trees, power outages and property damage, powerful storm surge for coastal areas, and significant early season wet snows for the higher elevations in the southwestern parts of the Mid Atlantic. This has the potential to be a dangerous and damaging storm, and should not be taken lightly. Locations in the path of the storm, especially along the coast, should pay close attention to this storm and take preparations. Stay tuned for more updates on Hurricane Sandy over the next few days.