Seattle's showers Friday may eventually influence 'Frankenstorm' next week

Photo of rainy Seattle on Oct. 26, 2012. (Photo: Puget Sound Clean Air Visibility Camera)

Our weather in the Pacific Northwest this weekend is going to be quite mundane by our standards -- just the usual late October rains. But did you know some of the energy from Friday's rain could eventually impact millions on the East Coast?

It's very subtle, but part of a weak upper level trough that is over the Northwest Friday is expected to race eastward across the nation over the weekend.

As it approaches the southeastern U.S., it's expected to intensify a bit and then its flow will help Sandy to turn to the north then northwest back toward the Atlantic Coast on Monday, National Hurricane Center forecasters wrote.

You can see this subtle development in this model animation that runs from Friday through Monday. It's showing the weather around 18,000 feet (500 mb).

Forecast models are still varying a bit on what will happen with Sandy, but you can excuse the models since this storm set up is probably unprecedented in at least modern meteorological record-keeping times.

The European model has moved Sandy more into the Delaware peninsula area, while the American "GFS" model has been painting an even more dire situation of bringing the incredibly intense storm right into the New York metro area, as this model shows from Friday morning (Valid 2pm EDT on Tuesday)

(Thanks to Twitter user @RyanMeud for this colorful version of the chart)

National and regional forecasters have quite a challenge on their hands not only in forecasting the monster, but how to communicate it, and they might have to break a few rules in doing so. Sandy is not going to be a traditional hurricane making landfall, but is going to undergo a transformation from a hurricane/tropical type storm to what's called an "ET" storm ("Extra-Tropical").

The difference is the source of the storm's energy. Hurricanes/tropical storms get their energy from the heat of warm ocean waters. ET storms get it from battle between warm and cold air masses. (Northwest storms are ET storms.) Sandy is going to transform from getting its energy from the Atlantic Ocean to tapping into the intense arctic air moving into New England from Canada and the Midwest.

(Incidentally, our great Columbus Day Storm of 1962 also underwent a similar transition from Typhoon Freda to an ET storm)

So while by hurricane standards "Sandy" may not really be one by the time it arrives on the East Coast, its impact could be on par with a Category 3 storm. It just won't act like a traditional hurricane -- in fact, the storm's wind speeds are expected to reach a far greater distance than traditional hurricanes.

Thus, forecasters have a challenge to communicate just how dangerous the storm is turning in to, even if Sandy is "only" a category 1 hurricane or so in the days leading up to its landfall. The Sandy of today will not be the Sandy of Monday.

Incidentally, forecasters will stick with the storm name Sandy even when it won't be a hurricane. National Hurricane Forecasters say they will note the storm in Public Bulletins as "Extra Tropical Storm Sandy"