Meteorologists watching the GFS weather model run from Sunday morning could hardly believe the output. Thousands of computations per second put together a 186 hour forecast, valid Monday morning October 29, 2012, that brings memories of the Blizzard of 1978, The Halloween Hurricane of 1991, and Hurricane Irene, all in one. Here it is..
How often are 186 hour forecasts correct? Great question, I'd give odds of 1 in 20 or so. As we get closer to Monday October 29th, the odds of accuracy increase. So we'll have to keep an eye on this potential severe storm. The map above is pretty much a worse case scenario.
What we see here is a 970 millibar low (possibly named Hurricane Sandy) centered about 200 hundred miles east of Cape Hatteras North Carolina. Most of the time a hurricane in this position is not a huge deal, as they are usually accelerating into the open Atlantic Ocean. But that is not the case on this map.
We have a merging, or phasing, of the polar & sub-tropical jet streams along the east coast. This would slow the storm and pull it toward the coastline. If this forecast comes true, we would be experiencing storm force wind from Maine to North Carolina. Slow moving tropical downpours would result in catastrophic flooding from Connecticut to New Jersey. There would even be potential for another major October snow storm for highest elevations from the Catskills to the Smokey Mountains.
How does this potential compare to the storms of 1978, 1991, and Irene of last August?
The two features that stand out most prominently are the 'loops' performed by the '78 and '91 storms. Each of those storms got caught under a Jet Stream that 'cut off' from the westerlies. Cut off storms result when upper level, and low level wind, both become a closed cyclones. Another description is 'vertically stacked', meaning surface storm and upper level storm become perfectly aligned on top of one another. Vertically stacked storms happen when the sub-tropical jet stream wave length and the polar stream wave length become aligned and then the separate upper level wind currents merge together, or 'phase'. This is where we come up with the blog title, 'East Coast Phaser Possible'.
The storms of '78, & '91 tracked north, then west, then south, then east again.. the result of becoming stacked and trapped under the cut off aloft. Think of it as getting stuck in a a rotary and going all the way around before you escape out and on to your net stop. Who can forget when this happened to the Griswold's? "Hey look kid's there's Big Ben, there's Parliament".
A 'retrograding' storm like this is usually a powerhouse that lasts more than one day. Here in New England, we have had more damage from cut off retrograding storms in the last few decades, than from hurricanes. We have to go back to the hurricanes of 1938, 1944, and 1954 for storms worse than the 3 day lashings of 1978 and 1991.
Last August 28, Hurricane Irene became and extra tropical storm as she 'phased' with the colder northern jet stream. Irene phased, but did cut off. All her damage was done in about 12 hours.
Here in 2012, we have great uncertainty in the forecast. But if the above GFS worst case forecast plays out.. we get the rainfall rate of Irene, and 3 day wind and waves similar to 1978 and 1991. It's something to consider, but not yet time to take action.
In the 18 hours since beginning this blog, the GFS is much less phased, no where near as alarming as the scenario just described.
Let's stay in touch though, 'just in case'.