After two very active Hurricane Seasons in terms of named storms with 19 each, 2012 is expected to be a little less active. However, there are some signs that it could prove to be more dangerous at the same time. Please note that the number of storms that form does not correlate to the number of landfalls or if those landfalls will be near you. Eg. 1992’s Hurricane Andrew a category 5 hurricane landfall in south Florida during a hurricane season with only 7 named storms, while Hurricane Irene (2011) made a category 1 landfall in North Carolina in a season with 19 named storms, no other hurricane landfalls occurred in the US in either year and so these storms will define the year.
Remember, it only takes one hurricane in your area to make it a bad season.
For 2012, I am forecasting an ‘active’ 15 named storms, 7 hurricanes, and 4 major hurricanes. (Give or take 1 in each category).
Factors that I’m considering for this forecast:
El Nino-Southern Oscillation (ENSO): This is a global scale weather phenomena that lasts one to three years. Defined as the temperature of the equatorial East Pacific compared to average, it comes in three phases; El Nino (warm), Neutral (average), and La Nina (cool). An almost three year long La Nina event recently came to an end and we are currently in a Neutral ENSO pattern. Seasonal forecasts are suggesting that it will stay Neutral or transition to a weak El Nino phase during the hurricane season.
In an El Nino phase, the sub-tropical jet stream is enhanced and the semi-permanent tropical upper-tropospheric trough (TUTT) is stronger. This means that wind shear across the Atlantic is greater than normal and so tropical waves, the precursors to tropical cyclones, have a harder time developing because their feedback mechanisms are disrupted by the wind shear. A La Nina phase has a much weaker sub-tropical jet stream and TUTT, and so wind shear is typically less of an issue. Neutral phases have characteristics of both El Nino and La Nina.
So, with a Neutral-weak El Nino pattern forecast for the Hurricane Season, it is likely that wind shear will remain near to slightly above average across the Atlantic.
Sea-Surface temperatures: Atlantic sea-surface temperatures have remained close to normal. The waters nearer to Africa are slightly cooler than average, while the waters of the Caribbean, Gulf of Mexico and Gulf Stream are slightly above normal. This means that African Easterly tropical waves early in the season will have a lower than average chance for development until they reach the Western Atlantic’s warmer waters. As a result, tropical cyclone numbers due to Cape Verde-type cyclones will be slightly suppressed.
However, because the Western Atlantic is above normal in terms of sea-surface temperatures, extra-tropical cyclones may have a better chance for transitioning into sub-tropical or tropical cyclones making up for lost seasonal totals. We have already seen this sort of development in the form of Tropical Storms Alberto and Beryl, and Hurricane Chris. Additionally, the warmth in the Caribbean allows for the monsoon trough that is typically over Central America to develop into tropical cyclones, this has contributed to the development of Beryl, and is currently being monitored for development of what would be named “Debby”.
Climatology: It can be argued that we have been in an active phase of Atlantic Hurricane activity, that began in 1995. This only loads the deck to allow a greater number of tropical cyclones to form. Finding a perfect analogue year isn’t ever going to happen as no two hurricane seasons are the same.
By the peak months of Hurricane Season tropical cyclones will be forming from all corners of the Atlantic; the monsoon troughs in the Caribbean, the stalled frontal boundaries in the West Atlantic, and the African Easterly Tropical Waves near the Cape Verde Islands. This year seems to favor the first two type of system based on the conditions set so far. This means that anything that does form will likely have little option but to affect land, but will probably be relatively weak because it formed so close to land.
Some other forecasts for this season (named storms, hurricanes, major hurricanes):
TWC (April 24, 2012)——————–11, 6, 2
UKMO (May 24, 2012)——————12, N/A, N/A
NOAA (May 24, 2012)——————- 9-15, 4-8, 1-3
FSU COAPS (May 30, 2012)————-13, 7, N/A
CSU (June 1, 2012)———————-13, 5, 2
TSR (June 6, 2012)———————-14, 6, 3