Hurricane Sandy is gearing up to bring ashore a smorgasbord of hazardous weather: Rip-roaring winds, flooding rain, crippling mountain snow, and a potentially devastating storm surge in some areas. This storm will impact 50-60 million people says NOAA.
Here are the images the tell the story.
This image shows projected wind speeds (from the GFS model) at an altitude of about 3,000 feet at 8 p.m. Monday night in knots. Notice they are near 90 knots over Washington, D.C. and Baltimore, and over 60 knots over the entire megalopolis from D.C. to Boston. Thankfully, winds at 3,000 feet translate to lesser values at the surface (where we live) - probably by about 25 percent. But - assuming this model is in the ball park - winds across the entire northeast I-95 corridor may well be gusting to 45-70 knots Monday evening, or 50-80 mph!
What would winds of 50-80 mph up and down the East Coast mean in terms of power outages? Researchers at Johns Hopkins University have developed a model for that:
Seth Guikema (pronounced Guy-keh-ma) and his team have developed a computer model built on outage data from 11 hurricanes to estimate the fraction of customers who will lose power, based on expected gust wind speed, expected duration of strong winds greater than 20 meters per second, and population density.
They find, conservatively, 10 million customers along the Eastern seaboard will lose power from Sandy. The image below indicates where outages are projected to be most highly concentrated.
Sandy is predicted to drop a ton of water: from 4-8” in the Washington, D.C. area to 5-10” over the Delmarva peninsula.
How historic would the amount of rain forecast be? Weather Decisions Technology (WDT) has prepared an analysis shown below. Its model projects Sandy to be a 500-to-1,000 year precipation event for some parts of the Mid-Atlantic with a 100-250 year precipitation event for broader areas mainly over the Delmarva peninsula. In the immediate Washington, D.C. area, it suggests a 1-10 year type event.
I would caution that the exact areas where the heaviest rain will fall is very difficult to predict. So while this map gives an idea of the historic potential of this event, the most extreme values will probably not coincide exactly where modeled here.
There is the possibility of a devastating 6-11 foot storm surge in Long Island Sound, Raritan Bay and New York Harbor. Low-lying areas of New York City (where evacuation orders have been issued) are likely to be flooded, and possibly parts of the subway system. Farther south, the storm surge will gradually decrease but major to severe coastal flooding is anticipated from the Mid-Atlantic on northward. This map shows a projection.
Several feet of snow are possible at high elevations in West Virginia, which would be record-breaking for this time of year. The map below shows one projection for snow totals from the NAM model. Couple these snow amounts with winds which may gust over 50 mph, and power outages are very likely in mountainous West Virginia. Heavy snow may fall in the mountains of southwest Virginia and western North Carolina as well.