Outlook for Hurricane Irma -- It could be bad. [View all]

[Binkie The Clown]

878 mb Storm Off North Florida — The Model Forecast for Irma that no one Wants to See Happen

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Looking beyond the official forecast, some of the our best long range model runs are putting together some seriously scary predictions for Irma. By next week, the Global Forecast System (GFS) model shows Irma as a 878 mb monster hurricane looming about 300 miles off Florida. 878 mb would represent the lowest pressures ever recorded in a hurricane in the Atlantic (The present strongest Atlantic storm was Wilma at 882 mb. The devastating Labor Day Hurricane hit 892 mb.). And it would almost certainly represent the strongest storm in our records ever to venture so far North. 878 mb roughly corresponds with maximum sustained winds in excess of 170 mph and possibly as high as 200 mph or more. And we’ve never seen something like that threatening the Central Atlantic U.S. East Coast in all of the modern era.

The model then slams the storm into Cape Hatteras just after midnight on Monday, September 11 as only a slightly weaker Category 5 range storm at 910 mb. The storm proceeds north into the Hampton Roads area early Monday morning retaining approximate Cat 5 status at 919 mb. After roaring over this highly populated low-lying region, the storm enters the Chesapeake Bay at 934 mb by noon on Monday — in the Category 4 range and still stronger than Hurricane Sandy — before crossing up the Bay and over the D.C. region by evening the same day at 958 mb (approx Cat 3).

To say this would be an absolute worst case disaster scenario for the Mid-Atlantic is an understatement. A storm of this intensity would produce 10-20 foot or higher storm surges, devastating winds, and catastrophic rainfall throughout the Outer Banks, Hampton Roads and on up the Chesapeake Bay. But unlike Harvey, it would be a fast-moving event. More like a freight train than a persistently worsening deluge.

This long range model scenario is not, however, an official forecast. It’s just what the GFS atmospheric computer models are presently spitting out. And such long range predictions from a single model, no matter how reliable, should be taken with at least a pinch of salt. That said, we should certainly, as the NHC recommends, keep our eyes on Irma and keep our response plans ready.