Post-Tropical Storm Sandy

Post-Tropical Storm Sandy   
October 29-30, 2012
National Weather Service - Baltimore/Washington

Updated: Nov 21, 2012
(note: this document may be updated as more information is analyzed for this event)

From a meteorologist's perspective, Sandy was a peculiar storm, in that it was transitioning from a hurricane to a winter storm as it was approaching land. That might seem like a minor thing, but the fuel that powers a hurricane (tropical ocean air) is entirely different from what powers a winter storm large differences in temperature across a region). Change the engine, and much like a car, you change the way a storm behaves entirely. Sandy had ways in which it behaved as a hurricane, but also ways it behaved as a winter storm. Its late October arrival also allowed all that tropical moisture to slam into cold, Canadian air, creating heavy snow - something very unusual with a tropical system.

Nationally, the most catastrophic impacts were in northern New Jersey, New York City, and Long Island, NY. That is because of the four threats that hurricanes can bring: flooding rain, tidal surge, winds, and tornadoes; the two that have the greatest potential to produce billions in damage and large loss of life are the tidal surge and hurricane force winds. Surge and winds were both at their worst in those areas. While the Mid-Atlantic did have both (and countless trees were felled across our region), the winds were worse to our north.

Due to the strongest winds being just above the surface with Sandy, winds were maximized at higher spots; even in our area. Winds gusted above 80 mph on the top of the Chesapeake Bay Bridge, 79 mph on top of Thomas Point Lighthouse on the Bay, and above 70 mph at Wintergreen ski resort on the Blue Ridge of Virginia.

Interestingly, the worst of the flooding rains were actually over our area. A swath of the Mid-Atlantic (including the Washington and Baltimore metro areas) saw a large amount of rain (5-12"). Baltimore had their 5th highest rainfall for any calendar day on record, and most for any day in October (6.67"). Meanwhile northern New Jersey and New York saw only about 2". Fortunately, our region had been rather dry before the storm, and the impacts of that deluge were less than they could have been if it had fallen on a soggy ground. None the less, road closures due to flooding were widespread late Monday into Tuesday.

It's hard to imagine 1-3 feet of snow in late October, but for many residents and travelers in the Appalachians and along the Blue Ridge (including Skyline Drive), that's exactly what happened. With all that tropical moisture pushing into cold, Canadian air, heavy wet snow was the result. One foot was logged on Skyline Drive at Big Meadows, and 2 feet was recorded at Bayard, WV. Power outages were widespread in the mountains from the combined impact of snow on the trees and very strong wind gusts (60-80 mph) along the ridges.

When a hurricane (or the remnant of a hurricane) impacts an area, there are always 4 threats that are possible - flooding rains, flooding from tidal surge, wind damage, and tornadoes (a special kind of wind damage).

Flooding Rains: Most common. Widespread rains inundate communities, and turn drainage ditches into raging rivers.

Tidal Surge: Along shorelines, it has the largest potential for loss of life and massive property damage.

Wind Damage: Creates power andcommunications outages, downed trees, and property damage.

Tornadoes: Causes massive wind damage in small, targeted areas.

Each tropical system brings its own level of impact for each of these four threats, but the primary threats come from this pool of 4. So, the next time a hurricane threatens, remember the threats and make your family ready (www.ready.gov).