The Tropical Meteorology Project at Colorado State University (CSU) just released its initial outlook for the 2012 Atlantic basin hurricane season. They expect a milder than normal storm season for the central Atlantic, Caribbean Sea, and Gulf of Mexico.
Sounds good right?
Now think back to 1992 when we only had 6 named storms, well below the average of 11.
<= This is Irene.
Andrew was the first named storm and only major hurricane of the otherwise quiet 1992 Atlantic hurricane season, but ….
Hurricane Andrew was a long-lived, destructive, classical, and very powerful Cape Verde-type hurricane of the 1992 Atlantic hurricane season and was only the third Category 5 hurricane to make landfall in the United States, after the Labor Day Hurricane of 1935 and Hurricane Camille in 1969.
Colorado State University meteorologists William Gray & Phil Klotzbach released the annual CSU Atlantic Hurricane predictions for their 2012 April report on 4/5/2012. They expect 2012’s June 1st to November 30th hurricane season to be less active. The scientists warn that “a slow season is no reason to breathe easy”, though.
CSU scientists forecast 10 named storm, 4 hurricanes, and 2 major hurricanes (winds greater than 111 mph winds). In typical years, 11 named storms, six hurricanes and two major hurricanes hit the Atlantic, Caribbean and Gulf of Mexico.
The projections for a milder 2012 season were based upon two main factors:
“Hurricanes thrive on warm water and the tropical Atlantic has cooled this year, …” and
There is a “… high likelyhood that an El Niño effect will develop this summer”.
El Niños (in the Pacific) create wind shear (strong winds at high altitudes) that makes it more difficult for tropical storms to grow into hurricanes.
The CSU team predicts that there is a 42% chance that at least one major hurricane will make landfall on the U.S. coastline vs this last century’s average of 52%.
Specific area risks: the U.S. east coast including Florida at 24% (average for last century is 31%) and the gulf coast from the Florida Panhandle westward to Brownsville at 24% (vs. 30% average for last century),
The report marks the 29th year for the CSU hurricane forecasting team, which is led by Philip Klotzbach and William Gray, but this was the first time for their forecast to include the probabilities of key factors affecting the hurricane season, versus previous simple numerical forecasts for the number of storms.
Details of the 2012 CSU Hurricane Report:
Klotzbach explains: “We have suspended issuing quantitative forecasts at this extended-range lead time in December, since they have not proved skillful in real-time over the last 20 years, …”. “One of the significant challenges in the early December prediction is that no statistical or dynamical models have shown skill at predicting El Niño – Southern Oscillation (ENSO) at this extended forecast lead time of 9-12 months, so we’re going to look instead at analyzing factors that influence the hurricane season rather than actually predicting the number of hurricanes.”
There is more reliable data available by April, so the CSU meterological group plans April forecasts, like this one, that identify the number of expected named storms, hurricanes and major hurricanes (Saffir/Simpson category 3-4-5). Additional updates of the 2012 Atlantic basin hurricane activity forecast are planned for June 1 and Aug. 3.
Previous December predictions were based on the two major factors known to affect the Atlantic basin hurricane season:
1) Atlantic thermohaline circulation (THC):
“When the THC is stronger than normal, a large variety of physical features in the tropical Atlantic are typically more conducive for hurricane formation and intensification. Tropical Atlantic water temperatures tend to be warmer, vertical wind shear (the change in wind direction with height) tends to be reduced, sea level pressures tend to be lower, and mid-levels of the atmosphere tend to be moister, all of which combine to create an environment favoring an active hurricane season.“
2) El Nino ~ The Southern Oscillation:
“When El Nino occurs in the tropical Pacific, it creates an environment less conducive for storm formation in the Atlantic. Typically vertical wind shear is stronger and the mid-levels of the atmosphere are drier in the tropical Atlantic in El Nino events, both of which are unfavorable for hurricane formation and intensification.“
2012 Atlantic Basin Hurricane Season Details:
• If there is no 2012 El Niño and the THC conditions continue at above-average conditions, (45% combined chance for this outcome), then hurricane activity will be approximately 40 percent higher than the average season. This translates to roughly 12-15 named storms, 7-9 hurricanes, and 3-4 major hurricanes.
• If there is a significant El Niño and the THC continues in the same above-average condition that has occurred every year since 1995 (30 percent chance of occurring), then tropical cyclone (TC) activity should be reduced to approximately 75 percent of the average hurricane season: roughly 8-11 named storms, 3-5 hurricanes, and 1-2 major hurricanes.
• If the THC becomes unusually strong in 2012 and no El Niño event occurs (15% combined chance), then TC activity increases by approximately 80 percent above the average hurricane season. This translates to roughly 14-17 named storms, 9-11 hurricanes, and 4-5 major hurricanes.
• If the THC becomes weaker (growing to only 40% of its normal strength) and a significant El Niño develops (10% combined chance), then there would be approximately 5-7 named storms, 2-3 hurricanes, and 0-1 major hurricanes.
As the annual weather cycles proceed to June and August, scientists then can identify the actual levels of the THC and El Niño events, and the CSU team will update their predictions. They accurately predicted 2011’s above-average hurricane activity for the Atlantic basin. In their June, 2011 forecast, the team called for 16 named storms, 9 hurricanes, and 5 major (Category 3-4-5) hurricanes. 2011’s events included 19 named storms, 7 hurricanes and three major hurricanes.
“There is significant uncertainty with this (December) earliest outlook, issued six months prior to the start of the hurricane season, so we’re looking more at a range of different potential outcomes which might occur,” Gray said. “We believe we’re still in an active multi-decadal period for hurricanes in the Atlantic basin.”
We look forward to their upcoming June and August updates.
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© Steven M. Fry