The East Coast Braces for Sandy
27-Oct-12
Hurricane Sandy is heading to the US East Coast; it is about 165 miles north of Great Abaco Island in the Bahamas, and about 335 miles southeast of Charleston, SC. Sandy was downgraded to a tropical storm earlier this morning for a few hours, but has re-strengthened and is now a Category 1 hurricane with 75 mph maximum winds. Little change in strength is expected over the next several days as Sandy transitions into a sub-tropical or extra-tropical storm. Sandy is forecast to turn to the northwest early next week, and head to the US mainland. There continues to be uncertainty in the timing and location of landfall, but the forecast models are tightening their spread and the most likely location at this time is around the DelMarVa (Delaware, Maryland, Virginia) peninsula to southern New Jersey. Because Sandy will be a very broad, intense extra-tropical storm by landfall, the impact is likely to be very widespread, and not confined to where the center crosses the coast.
Dry air and an approaching pressure trough from the west will affect Sandy over the next several days and cause a transition to a sub-tropical or extra-tropical storm. After this transition, Sandy may have a lower maximum wind, but it would be distributed over a much broader area and have a higher aggregate wind energy.
The models continue to reflect uncertainty in track projection, and while the current estimate for landfall is around Delaware, the uncertainty cone extends from the DelMarVa peninsula to Long Island, NY. As a broad extra-tropical storm, the exact landfall location is less important, and the potential impact of the storm will likely be wide spread along the US eastern coastline. Unlike a typical tropical system which moves swiftly as it approaches higher latitudes, a blocking pattern produced from the high pressure system in southeastern Canada will likely keep Sandy's forward motion relatively slow for storms of this latitude. This block could also cause the storm to slow significantly after landfall, resulting in several days of flooding rain in the Middle Atlantic States. Sandy is expected to cause storm surge of about 4 to 8 feet along Ocean city, MD to Connecticut-Rhode Island border.
Rainfall is expected to cause significant damage and disruption and the latest forecast indicates rainfall of over 12 inches for the 5-day period in Delaware and Maryland.
Hurricane Sandy Rainfall Forecast - October 27, 2012
Source: National Weather Service - Hydrometeorological Prediction Center
Track Forecast
There is a growing consensus among computer forecasting models that the track of Sandy will turn northwest into the US East Coast early next week. The track forecast models continue to reflect uncertainty in the projected track forecast for Sandy and show a spread of possible landfall locations between Virginia and Long Island, NY. The southern portion of a strong cold front and trough moving across the eastern US will initially steer Sandy to the northeast, keeping it well offshore of the southeast US.
However, because of strong blocking high pressure in the Canadian Maritimes, the northern portion of the trough will move very little. Most troughs steer tropical systems straying into the mid-latitudes toward the northeast and out to sea. This setup, a negatively tilted trough, will draw Sandy to the northwest, and back toward the US coast.
Hurricane Sandy Model Tracks - October 27, 2012
Source: Hurricane Forecast Model Output University of Wisconsin-Milwaukee
Intensity Forecast
Sandy is expected to remain near-hurricane strength while moving north into the mid-latitudes. Mid-latitude extra-tropical storms obtain their energy from strong contrasts between air masses (i.e., cold/dry air meeting warm/moist air) versus tropical systems like hurricanes that depend on extracting energy from very humid warm tropical air. As Sandy moves northward and this transition begins, its structure will change. Most noticeable of these changes will be that Sandy's wind field will greatly expand, and the highest winds will no longer be confined to near the center, as in a hurricane. Because of this expansion and spreading out of the core winds, the exact landfall point of the center becomes less important than for a true hurricane. The National Hurricane Center is estimating a 21% probability that Sandy will remain a hurricane at landfall in the US.
Hurricane Force Wind Speed Probabilities - October 27, 2012
Source: National Hurricane Center (NHC)
The blocking pattern is also allowing cold air out of Canada to be funneled south into the eastern US. This confluence of cold/dry and warm/moist air masses is the fuel needed to drive a strong nor’easter type extra-tropical cyclone, which is what Sandy should be as it moves into the US. The resulting storm system will also stay in the vicinity for several days as it winds down because of the blocking pattern at that latitude.
Hurricane Sandy Potential Storm Track - October 27, 2012
Source: National Hurricane Center (NHC)
At 8 am EDT today, Saturday, October 27, the center of Sandy was located about 165 miles north of Great Abaco Island in the Bahamas (near latitude 28.8N, longitude 76.8W) and was roughly 335 miles southeast of Charleston, SC. Maximum sustained winds were 75 mph, making Sandy a minimal Category 1 hurricane.
The storm is moving to the north-northeast at 10 mph with a turn to the northeast expected over the weekend. On this forecast track, the center should remain well offshore of the southeast coast US. Early Monday morning, October 29, the center of Sandy is forecast to be roughly 200 miles east of Cape Hatteras, NC. At that time, Sandy should begin to be drawn northwestward into the negatively tilted trough, steering it into the Mid-Atlantic Coast of the US mainland. Maximum winds at the projected time of landfall are expected to around 75 mph, and the official forecast track has the center of Sandy moving inland into Delaware late Monday night, or early Tuesday morning, October 30.
Hurricane force winds extend out some 100 miles from the center of Sandy, and tropical storm force winds out to 450 miles from the center. Tropical storm warnings are effect for the eastern coast of Florida from Brevard County, north to St. Augustine, and for the northeastern half of the South Carolina coast and for all of the North Carolina coast.
EQECAT will continue to monitor this event and provide updates as more information becomes available.
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