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Irene's rains heaviest on record in Vermont; Tropical Storm Katia forms

By: Dr. Jeff Masters, 3:40 PM GMT on August 30, 2011

Record flooding continues in the Northeast from Irene's torrential rains. Hardest hit was Vermont, where heavy rains in the weeks prior to Irene's arrival had left soils in the top 20% for moisture, historically. Irene dumped 5 - 8 inches of rain over large sections of Vermont, with a peak of 11.23" at Mendo. The reading from Mendo was the greatest single-day rainfall in Vermont's history, according to wunderground's weather historian Christopher C. Burt, beating the 9.92" that fell at Mt. Mansfield on 9/17/1999 during the passage of Tropical Storm Floyd. The 13.30" that fell on East Durham, NY during Irene was just shy of New York State's all-time 1-day rainfall record: 13.70" at Brewster on 9/16/1999, from Tropical Storm Floyd.

Figure 1. Wunderphotographer 43BJAGER recorded this image of a house in Sharon, Vermont, that started out the week on the other side of this underpass.

According to the final Hurricane Irene summary from the NWS, the storm dropped 20" of rain in two locations, one in North Carolina and one in Virginia. Here are the highest rain amounts from the hurricane for each state:

Virginia Beach, VA: 20.40"
Jacksonville, NC: 20.00"
East Durham, NY: 13.30"
Freehold Twp, NJ: 11.27"
Mendon, VT: 11.23"
Ellendale, DE: 10.43"
New Hartford, CT 10.15"
Baxter St. Park, ME: 9.91"
Savoy, MA: 9.10"
Lafayette, PA: 8.82"
Pinkham North, NH: 7.33"
Warren, RI: 5.37"

Tropical Storm Katia forms
Tropical Storm Katia formed this morning in the far Eastern Atlantic off the coast of Africa. Katia will be in a moist, low wind shear environment with ocean temperature 1 - 2°C above the threshold needed to support a hurricane, and should be able to intensify to major hurricane strength when it passes to the north of the Lesser Antilles Islands 5 - 6 days from now. It is possible that some of the outer spiral bands of the storm might bring heavy rain squalls to the northern Lesser Antilles, but it would be a surprise if the core of the storm passed through the islands. The long term fate of Katia is unknown. Dr. Bob Hart's Historical Tropical Cyclone Probability web page suggests shows that tropical storms in Katia's current position have a 19% chance of hitting North Carolina, a 16% chance of hitting Canada, an 11% chance of hitting Florida, and a 47% chance of never hitting land.

Figure 2. The morning run of the GFS Ensemble prediction. The ensemble prediction was done by taking a lower-resolution version of the GFS model and changing the initial distributions of temperature, pressure, and humidity randomly by a few percent to generate an ensemble of 20 different computer projections of where Katia might go. The operational (highest-resolution) version of the GFS model (white line) is usually more accurate, but the ensemble runs give one an idea of the uncertainty in the forecast.

Katia is the 11th named storm this year, and comes a full twelve days before the half-way point of the Atlantic hurricane season. Climatologically, September 10 marks the half-way point. A typical hurricane season has just 10 - 11 named storms, so we've already had a whole season's worth of storms before reaching the half-way point. At this rate, 2011 will see 25 named storms, making it the 2nd busiest season on record, behind 2005. Katia's formation date of August 30 puts 2011 in 5th place for earliest date of arrival of the season's 11th storm. Only 2005, 1995, 1936, and 1933 had an earlier 11th storm.

Gulf of Mexico development possible late this week
Several of our best computer models for predicting formation of tropical cyclones, the GFS and ECMWF, are predicting that an upper level pressure interacting with a tropical wave now over the the Western Caribbean could combine to spawn a tropical depression in the Gulf of Mexico late this week or early next week. The formation location is likely to be off the coast of Louisiana or Texas, but the track of the system is hard to predict at this point.

Figure 3. Portlight volunteer Thomas Hudson clears a driveway yesterday in Hollywood, Maryland.

Portlight disaster relief effort in Maryland
Hurricane Irene heavily damaged the town of Hollywood, Maryland, when a tornado cut off electric power, water, and phone service. Portlight and Team Rubicon volunteers arrived before emergency personnel, after following up on a local tip. What they found was an isolated area whose plight was unknown to the larger community. Most residents were trapped at their homes by heavy debris. Portlight and Team Rubicon worked for two days to clear paths to each address, extract vehicles from debris, and cut down trees that constituted safety hazards. Portlight also instructed local residents how to operate and maintain chainsaws and safely clear debris. No other volunteer organizations or emergency personnel arrived at any time, and Portlight succeeded in meeting the specific needs of the underserved, unserved, and forgotten. Visit the Portlight blog to learn more; donations are always welcome.

I'll have a new post on Wednesday discussing if the evacuations and media hype surrounding Irene were excessive.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.