Although the Atlantic hurricane season in 2010 tied for the third most active on record, few noticed as storms largely avoided the U.S. mainland. In its preseason outlook released this morning, AccuWeather cautioned that the risk of U.S. landfalling storms is higher during 2011 despite its prediction for fewer storms.
The State College, Pa.-based company is projecting 15 named storms from June 1 to November 30, eight of which will become hurricanes, and three major hurricanes (category three or higher). Last year (2010), there were 19 named storms, 12 hurricanes and five major hurricanes wheras Accuweather predicted 15 named storms, five hurricanes, and two or three major hurricanes.
A declining La Nina is the primary reason AccuWeather predicts somewhat less activity than last year. Hurricane activity is usually elevated during La Ninas as they tend to feature weaker westerly winds that are hostile to developing storms.
“[La Nina] is now starting to taper off a little bit,” said Ken Reeves, director of forecasting operations at AccuWeather. “But we think it will be strong enough early on for an above average type of year. If La Nina went to neutral quickly, it might squash some of the storms especially as the season wears on.”
AccuWeather’s prediction for more U.S. landfall risk relative to last year is based on the idea that atmospheric pattern - that persistently steered storms out to sea - will not align in the same configuration. Reeves conceded last year’s landfall forecast from AccuWeather which called for “above-normal threats on the U.S.” didn’t work out.
“The numbers were right but the impacts were wrong,” Reeves said.
AccuWeather forecasts the landfall risk to evolve geographically as follows in 2011:
This year, the early season threat area will be the western Gulf of Mexico and the southern portion of the Caribbean. Within this zone, the higher concern for landfalls will be along the Texas and Louisiana coastlines
As for the mid-to-late season zones, the eastern Gulf and Caribbean will be the focus. The higher concern areas will be the Florida Peninsula to the Carolinas.
Another mid-to-late season concern for landfalls will be northern New England and the Canadian Maritimes.
Reeves cautioned that this landfall forecast was tentative.
“We’d like to see what happens in the next six weeks, where precipitation starts to fall, what the predominant upper pattern is over the U.S,” he said. “That will dictate where the ridges [that steer storms] set up.”
AccuWeather will release a revised pre-season outlook in six to seven weeks.
Former AccuWeather chief forecaster Joe Bastardi (now at WeatherBell), who led last year’s outlook for AccuWeather, blogged today that “there is a ramped up threat on the U.S. coast” - consistent with his previous employer’s forecast.
Some forecasters do not believe there is not much, if any value in the kind of outlook AccuWeather and Bastardi are providing. Last year, Senior Meteorologist Stu Ostro at the Weather Channel wrote:
“They’re [the outlooks are] still useless in the sense that nobody can predict with confidence and accuracy exactly what will happen in any given community. The devil is in the details, and we don’t know exactly what the outcome of the season will be in Houston or New Orleans or Miami or Myrtle Beach or New York City or any big city or small town between Brownsville, Texas and Eastport, Maine in the U.S., or for any given location in the world which is susceptible to tropical cyclones.”
But Reeves believes certain elements about the seasonal risk can be identified in advance, even if not consistently.
“I’m not sure every year you can provide hang your hat on the exact value, but you can provide some information regarding some levels of decreased or enhanced areas of risk,” he said.
Update (2:40 p.m.): Capital Weather Gang’s tropical weather expert Dr. Greg Postel sent in the following comment on AccuWeather’s outlook--
In general, the hurricane forecasts offered to us long before the season starts have ... so far ... not shown much skill. They do, however, offer a glimpse of what the atmosphere and ocean might look like during those critical months when hurricane development most sensitively depends on how the two are arranged. As AccuWeather’s outlook appropriately mentions, this year we can reasonably expect a near-neutral ENSO condition during the hurricane season (neither strong El Nino nor strong La Nina), and warmer than average surface waters over much of the tropical Atlantic. As in all years, but perhaps moreso this time around given these conditions, the fertility of this year’s tropical breeding grounds will be very sensitive to local environmental patterns that vary on an intraseasonal (weekly or monthly) basis. Some of these factors, as Accuweather points to, are indeed related to the high pressure systems over the Atlantic Basin and the humidity/dustiness of the tropical atmosphere. It turns out that a big player in these week-to-week variations is related to the phase of the Madden Julian Oscillation (MJO). The MJO is a tropical weather system the size of an entire ocean basin. It is intricately involved with varying the wind, temperature, cloudiness, and rainfall in the hurricane development regions. However, it’s too early to get a reliable handle on how these conditions will vary locally when a tropical disturbance is in its formative stages. This is one of the problems with relying too heavily on hurricane forecasts made in early spring (or before). As Stu Ostro correctly points out, “The devil is in the details”.
Irrespective of the reliability of seasonal outlooks, Reeves highlighted the dangers these storms pose to portions of the Atlantic coast , many of which haven’t experienced a destructive storm in decades.
Concerned about complacency, he said:
“People build on these barrier islands and expect nothing to happen during their lifetime. I am fearful there is going to be a larger damage result form a storm at some point over next 5-10 years than what happened during Katrina from damage even if not from lives. We can evacuate the coast. The problem is the property stays behind.”