Thursday, December 10, 2009

Above average hurricane season predicted for 2010

Remember the Pacific Decadal Oscillation?
After a 23 consecutive month string of negative values the PDO went warmer in August. That string was the longest since the PDO entered it's 30 year warm phase in 1977. It appears that the PDO will be returning to negative values shortly (see Sea Surface Temperature anomaly map, below) which implies fewer El Nino's/ more La Nina's.*
From Ken Kaye's Storm Center:

William Gray and Phil Klotzbach call for an above average hurricane season next year.

They predict 11 to 16 named storms, including six to eight hurricanes. They forecast three to five of the hurricanes will be major with sustained winds greater than 110 mph.

An average season sees 11 named storms, including six hurricanes, two major.

The main reasons behind their projections: El NiƱo, the atmospheric condition that suppresses storm formation, is expected to dissipate before the season starts; and sea surface temperatures in the tropical Atlantic should be warm.

As part of their seasonal forecast for 2010, released this week, the Colorado State University forecasters also project:

-- A 64 percent chance that at least one major hurricane will strike the U.S. coastline in 2010. The long-term average probability is 52 percent....MORE

Here's the latest SST anomaly map from Unisys Weather:

Current Sea Surface Temperature Anomaly Plot

�Unisys Corp. 2001

*Wolter’s Multivariate ENSO Index indeed shows a greater frequency of El Ninos (positive MEI values in red) during the warm phase and the opposite, more La Ninas in the cold phase (negative MEI values in blue), when the reverse of the sea surface anomaly pattern above dominates.

Figure 6: Wolter’s Multivariate ENSO Index (MEI) plotted since 1950. Cold phase of the PDO lasted until 1976 followed by the warm phase. The more significant positive spikes (red) are El Ninos and negative (blue) La Nina

This shows about twice as many El Ninos as La Ninas during the positive PDO and nearly three times as many strong El Ninos and La Ninas. The opposite occurred during the prior cold PDO regime.