Last year the Atlantic and Caribbean hurricane season was way more active than normal just as predicted, but luckily there were no big land strikes by the 19 tropical cyclones that formed and the twelve hurricanes. The 2010 season had the most named storms since 2005 and tied for third place (with 1995 and 1887) for most named storms in history and tied with 1969 in second place for the number of hurricanes in a season.
What about this year? Expectations for this season back in the winter were for a much less active season than last year, but still above-normal. The changes occuring with the La Nina and model projections for it to become near-neutral or even weakly Nino-ish, along with changes in the QBO are making it more difficult to fortell the 2011 tropical cyclone season for the Atlantic.
Right now I have a long list of possible analog years. It will have to be whittled down as spring signals become more apparent.
We are still in the cold negative phase of the PDO and warm positive phase of the AMO. But Atlantic temperatures are nowhere near as warm as last season thanks to the cold east winter from the strong negative NAO. This will be a summer and fall following a strong La Nina, but also it is a second year La Nina. As I said, there is much uncertainty regarding Pacific Ocean wind shear contributions based on the ENSO state question mark.
Some but not all of the analog years I am looking at ( in no particuliar order) are: 1996, 1999, 2000, 2008, 1956, 1961, 1989, 1976, 1974, 1955, 1950, and 1971.
The average number of named storms in that analog set is: 12 with a low of 8 in 1956 and a high of 16 in 2008.
I further note that the December “Dr. Gray” CSU team analog forecast was 11.6 and their statistical scheme was 14.8. Their actual December call was for 17. They will update this on April 6th and again in June and August. Since we entered the positive phase of the AMO in 1995 the seasons have averaged 15, and the average for a second year cold ENSO is close to 15 named tropical cyclones.
My current analog-weighted early range forecast is for 12-15 named systems. I will not attempt a break down of types or intensity at this early time.
I will point out that the Private U.S. firm WSI has predicted 17 named storms, 9 hurricanes, 5 of those being intense. This is an exact match to the CSU Gray team December forecast.
The Private British firm Tropical Storm Risk is calling for 16 named cyclones, 8 hurricanes, 4 of those being intense. They predict two hurricanes and 3 tropical storms will make landfall somewhere along the U.S. Coastline. I must point out that I have yet to see any skill shown by any source when it comes to strike locations. Modest skill is demonstrated regarding prediciton of the seasonal numbers. EDIT: On March 27th the private U.S. forecasting firm Accu-weather issued its first forecast and predicted 15 named storms with the highest risk to TX, South FL, and the Carolina coasts.
And on March 22 tropical forecaster Jeff Masters posted this research: It is well-known that when an El Niño event is in place, a significant reduction in Atlantic hurricane activity results due to an increase in wind shear. With La Niña likely gone by June, what are the chances of having El Niño in place by the August-September-October peak of hurricane season? Well, our long-range El Niño models do a poor job of making accurate predictions in the spring, a phenomena known as the “spring predictability barrier.” True to form, the March predictions by these models are all over the place (Figure 1.)
There are 5 predictions for La Niña conditions being present during the upcoming hurricane season, 7 predictions for neutral conditions, and 5 predictions for El Niño. If we look at past history, since 1950, there have been six La Niña events that ended in the spring. During the subsequent hurricane season, two of those years experienced El Niño conditions: 1951 (10 named storms, 8 hurricanes, and 5 intense hurricanes) and 1976 (10 named storms, 6 hurricanes, and 2 intense hurricanes.) The other four years had neutral conditions during hurricane season. These years were 1968 (8 named storms, 5 hurricanes, 0 intense hurricanes), 1989 (11 named storms, 7 hurricanes, 2 intense hurricanes); 1996 (13 named storms, 9 hurricanes, 6 intense hurricanes); and 2008 (16 named storms, 9 hurricanes, and 5 intense hurricanes.) So, three of these six analogue years had five or more intense hurricanes (including one of the El Niño years).
Looking at sea surface temperature in the hurricane main development region (MDR), the stretch of ocean between the coast of Africa and Central America, including the Caribbean, February temperatures this year were 0.62°C above average, the 7th highest February anomaly since the late 1800s. Of the six analogue years since 1950 when La Niña ended in spring, only 1996 had a much above average February SST anomaly in the MDR (0.61°C.) Thus, I believe it is a reasonable speculation at this point to predict this year’s hurricane season will be similar to 1996, with its 13 named storms, 9 hurricanes, and 6 intense hurricanes–assuming we end up with neutral and not El Niño conditions this fall.
The 1950-2009 climate averages are: 10 named storms, 6 hurricanes, 2 intense.
At least statistically speaking it would be unheard of to go more than five years without a major U.S. landfalling hurricane.