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Posted at 04:35 PM ET, 10/30/2012

Was Hurricane Sandy well-forecast? Was it over-hyped?


NOAA’s GOES-13 satellite captured this visible image of Post-Tropical Sandy rolling inland on Tuesday, Oct. 30 at 6:02 a.m. EDT. (NASA)
Did Hurricane Sandy live up to the hype? That’s a debate raging amongst Washingtonians.

The record shows forecasts for this extraordinary weather event were quite good, although the impacts from the storm’s winds were not as bad as feared.

The amount of lead time forecasts provided for this event was exceptional. In fact, I first alerted readers about the potential for a major storm on October 21, more than a full week before it struck.

From that day to the day the storm struck, we were guided by the European Centre for Medium Range Forecasting (ECMWF) computer model, which provided exceptionally reliable and consistent long-range and short-range simulations for this storm.

Some storms are more predictable than others. This one proved fairly predictable.

The ECMWF model snuffed out the storm potential on Sunday, October 21. After reviewing it, here’s the message I posted to the Capital Weather Gang Facebook group that day, accompanied by the model simulation graphic below:

Big storm early next week (Oct 29) with wind and rain??? A number of computer models today were hinting at that, suggesting a tropical system now in the Caribbean may merge with a cold front in that time table, close to the East Coast. At the same time, 8 days is an eternity in storm forecasting, so plenty of time to watch this. Consider this an early “heads-up” that we’ll have an interesting an weather feature to monitor this week... details on what to expect and whether we’ll even deal with a storm still way up in the air.


ECMWF model simulation of Sandy for Monday October 29 made Sunday morning October 21. It was not far off. (StormVistaWxModels.com)
Beginning Monday, October 22, we discussed the possibility of this storm and explored its explosive potential. Each day, our confidence grew that a powerful storm would affect the region, even as the exact track of the storm remained uncertain. We used words like “monster”and “mega-storm” to describe it and said it could be “unprecedented in East Coast storm history.”

It turned out to be all of these things, becoming one of the largest Atlantic hurricanes on record while setting records for minimum low pressure (an indicator of storm intensity) in Atlantic City, Philadelphia, Baltimore and Hagerstown, Md among other locations.

As the arrival of the storm drew closer, we began to discuss track scenarios - starting with four on Thursday, October 25 before narrowing it down to one on Sunday, October 28. (Note the scenario we described as having the highest likelihood on that Thursday - a landfall north of the Delmarva peninsula but south of New England - turned out to be correct).

Our detailed Sunday forecast - which described exactly what we thought would happen - was also on the mark, though we missed on a few details.


Capital Weather Gang’s forecasts for peak winds and total rainfall amounts issued midday Sunday for Hurricane Sandy.
Our total rainfall prediction was on target as we called for 4-7 inches in the metro area, which is about what fell.

Our forecast of peak wind gusts of 55-65 mph was also on the mark. However, we later referred to forecasts from the National Weather Service which called for gusts up to 70-80 mph, which - except for some isolated reports - were too high.

But we can’t really kick ourselves or criticize the National Weather Service for mentioning the possibility winds might gust above 70 mph. Models indicated their potential and had they been more widespread and their potential ignored, people would have been caught off-guard. Instead, we were as ready as we could be for such winds and were fortunate they did not materialize except in a few instances.

In the end, we said Sandy could be very bad for the D.C.area but not the worst case. For example, we cited a few reasons why we didn’t think impacts would be as bad as the derecho. We said if the derecho was a 10 on a 1-to-10 impact scale, then this would be more like an 8, but just an estimate.

In the end, Sandy was more like a 6 or 7, because: 1) we were relatively prepared 2) top wind gusts were about 10 mph less than they might have been, largely due to the track of the storm to our north and the fact our wind was blowing off the land rather than the water, and 3) the power grid was in better shape compared to June.

If one nit picks, they might point out the wind estimates given in our timeline were too aggressive. Strong winds started later than we predicted and ended earlier. This also played a role in the smaller impact over our area.

How would you grade our forecast and pre-storm coverage of Sandy?

By  |  04:35 PM ET, 10/30/2012

Categories:  Latest, Tropical Weather

 
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