Monday, September 27, 2004
Weather columnist Kevin Myatt: Three reasons why flooding happened in Southwest Virginia
Kevin Myatt is The Roanoke Times' weather columnist.
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(1) Tropical Depression Jeanne -- the former Hurricane Jeanne of Florida infamy and Tropical Storm Jeanne of Haiti tragedy -- moved much farther west than expected, passing almost directly over Roanoke at midday Tuesday. This caused much more heavy rain associated with what was formerly the hurricane's northern eyewall to move directly through the area.
(2) The storm's path allowed winds out of the east to draw additional moisture out of the Atlantic and carry that moisture up the eastern slopes of the mountains, squeezing it out as it was lifted -- the upslope effect.
(3) A stationary front parked across the area, allowing a cooler, more stable air mass to the west to collide with the sticky, tropical air mass to the east. This allowed more moisture to condense into torrential rain. Being slightly on the cool side of the front, it did at least dampen severe weather potential, eliminating the tornado threat for the immediate Roanoke area. But the moist air overriding the cool dome on east winds squeezed it out like a sponge.
On Monday, Jeanne might have missed being a major weather event in Southwest Virginia. Those factors:
(1) Its expected path southeast of us. Usually, the heaviest rain is on the northeast side of an inland tropical system.
(2) Since we didn't get the torrential rain we feared in Ivan, and even what we did get was 10 mostly dry days ago, the rivers and creeks are not as full as they were and the ground is not as saturated as it was after Frances. It's not dry, but it will take a bit more to set off major flooding than it would have with Ivan. The National Weather Service is estimating that about 3 inches will start flooding creeks in most areas.
(3) Jeanne will be moving much faster than Ivan. It will not dilly-dally and then spin back around and have an offspring like Ivan. Jeanne should be off the coast of Newfoundland by Thursday.
Factors (as seen on Monday) for Jeanne being a major weather event for us:
(1) Jeanne has so far been closely following Frances' track, and Frances did dump a lot of rain on us.
(2) We will be trapped between Jeanne and a cold front, and this collision of air masses often sets up a boundary that squeezes out a lot of rain. This is what happened to Ohio, West Virginia and the Pittsburgh area with Ivan.
(3) Easterly winds ahead of Jeanne are always a threat to draw more moisture from the Atlantic and send it uphill, squeezing it out over our mountains. This is what happened with Frances, but never really got cranking with Ivan.
A good weather geek guess: 1-2 inches of rain in Roanoke, more to the east, less to the west, with isolated much higher amounts along ridge slopes. The official 48-hour rainfall forecast.
Hurricanes do strike the same place twice
Future Jeopardy answer: Latitude 27.2 North, Longitude 80.2 West.
Future Jeopardy question: Where did both Hurricane Frances and Hurricane Jeanne officially make landfall within three weeks of each other in September 2004?
The south end of Hutchinson Island, near Sewall's Point, or just east of Stuart might also be acceptable answers to this soon-to-be-historic meteorological question.
Two hurricanes hitting the same 100-mile section of coast in the same season is rare. But two whose eyes cross the same point within three weeks of each other — in a stretch of coastline unmarred by major hurricanes in the 20th century — is unthinkable.
The unthinkable is reality.
This Atlantic tropical season is one for the books, certainly the most active since 1995 when we went all the way to the "T" storm in the alphabetical list — though most of those were far out in the Atlantic, not near the United States. We're
1995 got close to a Frances-Jeanne event when Erin and Opal targeted the same narrow section of coast near the Alabama-Florida border — very near where Ivan came ashore this year. But the Erin-Opal tag-team strike wasn't nearly as pinpoint precise as Frances-Jeanne, nor was it as close in time. Erin and Opal were two months apart.
It's been a season where ocean and atmospheric conditions have been favorable for rampant and rapid tropical development, and atmospheric features have continually forced the storms toward the United States — specifically Florida — rather than allowing them to turn out to sea. Though El Nino is brewing warm water temperatures in the Pacific, this development has not as yet turned the spicket down on the Atlantic tropical season as it often does.
If there is some good news for four-times-bitten Florida, it's that we are now past the historic peak of Atlantic hurricane season when the chances of development lessen with each day. Those chances don't become negligible until at least Thanksgiving, and there is another month of typically active tropical weather to get through yet. So, yes, it is possible that Florida could still get its record-breaking fifth hurricane landfall.
What could be good news for many of you is that there are serious signs that fall-like cool air, maybe even frosty weather, will begin arriving late this week. Yes, there are other things happening in the weather besides tropical storms and hurricanes. A re-arranging weather pattern over the continental U.S. could nudge the weather pattern a bit, perhaps forcing any new tropical systems to go out to sea. This is yet to be determined.
But for now, we have at least one more tropical scrape to get through here in western Virginia tonight and Tuesday as the remnants of Jeanne make a close encounter. See above for a breakdown of the possibilities.




