Helene a major hurricane

Hurricane Helene continues to intensify, and is now the season's second major hurricane. Helene is over warm waters of about 28C, and under about 10-15 knots of wind shear. These conditions favor intensification for another two days, and Helene could be the first Category 4 hurricane in the Atlantic this year. Helene is currently headed more north than west, following a cut little brother Gordon has made through the Bermuda High. However, this cut is expected to close up later today, and the Bermuda High will re-establish itself and force Helene more to the west. By Wednesday or Thursday, a strong trough of low pressure will be moving off the East Coast and should turn Helene more to the north. It remains to be seen if this trough will be strong enough to finish the job and fully recurve Helene. If not, the Bermuda High will build back in, forcing Helene more to the west again, and potentially allowing it to strike the Mid-Atlantic or New England coasts of the U.S., or the Maritime Provinces of Canada. The models are VERY fuzzy at these long time scales, but the odds are that Helene would have yet another trough of low pressure to contend with before she could strike the coast. The computer models in general have performed poorly with the long-range track of Helene, and I am putting more stock in the historical record of what similar hurricanes have done in the past. I modified historical map of hurricanes to include all Category 1-5 hurricanes passing within 300 miles of Helene's current position. This map offers us some reassurance that Helene will probably not make landfall in the U.S. or Canada--only one of the 16 storms plotted have done so, and this storm <>a href=http://www.wunderground.com/hurricane/at200309.asp(Isabel, 2003) started further south than Helene's current position. I still put Helene's chances of a U.S. landfall at about 10%. Bermuda is at considerably higher risk, but the storm is still too far away to have a very good idea of this risk. Bermuda is a small target, and the five day track forecast errors are on the order of 350 miles.


Figure 1. Current satellite image of Helene, updated every 1/2 hour.

Mexico cleans up from Hurricane Lane
Mexico is cleaning up the damage from Hurricane Lane, which made landfall at 12:15pm PDT Saturday as a powerful Category 3 hurricane with 125 mph winds. However, Lane struck a sparsely populated region of the Mexican coast about 50 miles northwest of Mazatlan, and damage was mostly limited to washed out roads, toppled power lines, and at least one destroyed bridge. The storm surge of approximately six feet affected only an uninhabited barrier island and some adjacent farmland, and did very little damage. The extreme Category 3 winds of the eyewall affected an area of coast about 20 miles wide and stretching 20 miles inland. Only a few hundred people lived in this region.

The rest of the tropical Atlantic
Hurricane Gordon is still out there, but is no threat to land. A non-tropical area of low pressure a few hundred miles east of Cape Hatteras, North Carolina, has a slight chance of development as it drifts slowly east. Shower activity has decreased in this system this morning. Some of the computer models are forecasting that a tropical wave moving off the coast of Africa today will develop into a tropical storm later this week.

Typhoon Shanshan
In the Western Pacific, Typhoon Shanshan made landfall Sunday in southwestern Japan as a Category 1 storm. Shanshan killed nine and injured over 280 in Japan. Its powerful winds were able to lift a train off its tracks and lay it on its side. The typhoon brought the ninth strongest winds to the Korean peninsula in history, according to the Korea Meteorological Administration. Wind gusts reached 164 km/hr (102 mph) on Korea's Ullung Island as it passed by. Shanshan, the Chinese-language name for a young girl, was the 13th typhoon of the Western Pacific season.

Remainder of hurricane season outlook
I posted my outlook for the remainder of hurricane season Friday, in case you missed it.

I'll have an update Tuesday morning.
Jeff Masters