June 2012 conditions in the Atlantic
In June, strong upper-level winds tend to create a shearing force on tropical storms (wind shear), which tears storms apart before they can develop. In a typical June two branches of the jet stream, the polar jet to the north, and a subtropical jet to the south, bring high levels of wind shear to the Atlantic Ocean. The southern subtropical jet currently lies over the Caribbean Sea, and is expected to remain there the next two weeks, making development unlikely in the Caribbean.
In May, between the two branches of the jet stream, a hole or relatively calm area in the wind shear pattern formed off the Southeast U.S. coast, and this is where both Tropical Storm Alberto and Tropical Storm Beryl were able to form. Their formation was aided by the fact ocean temperatures off the U.S. East coast are quite warm--about 1 - 2° C above average. A wind shear hole is predicted to periodically form during the next two weeks off the Southeast U.S. coast, making that region the most likely area of formation for any first-half-of-June tropical storms. However, none of the reliable computer models are predicting tropical storm formation in the Atlantic between now and June 8.
May ocean temperatures in the tropical Atlantic are approximately the third coolest recorded since the current active hurricane period began in 1995. Tropical storm activity in the Atlantic is strongly dependent on ocean temperatures, and the relatively cool temperatures imply that we should see a delayed start to development of tropical waves coming off the coast of Africa and moving into the Caribbean, compared to the period 1995 - 2011.
An interesting feature of this month's sea surface temperature departure from average is the large area of record-warm ocean temperatures off the mid-Atlantic and New England coasts, from North Carolina to Massachusetts (graphic above). Ocean temperatures are 3 - 5°C (5 - 9° F) above average in this region. This implies waters of much above-average warmth will likely be present during the peak part of hurricane season, increasing the chances for a strong hurricane to affect the mid-Atlantic and New England coast.
The upper-level jet stream pattern is critical for determining where any tropical storms and hurricanes that form might go. Today, these steering currents are in a typical configuration for June, favoring a northward or northeastward motion for any storms that might form. However, steering current patterns are difficult to predict more that seven days in advance, and there is no predicting how the steering current pattern might evolve this hurricane season.
2012 might experience a pattern like that which occurred during 2004 - 2005 (above), with a westward-extending Bermuda High Pressure system, forcing storms into Florida and the Gulf Coast. Or, it is possible that a pattern similar to 2010 - 2011 could develop, with the large majority of the storms recurving harmlessly out to sea.
Colorado State predicts a slightly above-average hurricane season
A slightly above-average Atlantic hurricane season is predicted for 2012, according to the seasonal hurricane forecast issued June 1 Colorado State University (CSU). The CSU team is calling for 13 named storms, 5 hurricanes, and 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 80, which is 87% of average. This is very close to the 1981 - 2010 average of 12 named storms, 6 hurricanes, and 3 major hurricanes. The forecast calls for an average chance of a major hurricane hitting the U.S., both along the East Coast (28% chance, 31% chance is average) and the Gulf Coast (28% chance, 30% chance is average). The risk of a major hurricane in the Caribbean is also average, at 39% (42% is average).
The CSU teams expects we will have a weak El Niño develop by the peak of this year's hurricane season in September, which will minimize this year's activity by increasing wind shear over the Tropical Atlantic. However, there is considerable uncertainty in this outlook.
How accurate are the June forecasts?
The June forecasts by the CSU team between 1998 and 2009 had a skill 19% - 30% higher than a no-skill climatology forecast for number of named storms, number of hurricanes, and the ACE index. This is a fair amount of skill for a seasonal forecast, and these June forecasts can be useful to businesses such as the insurance industry and oil and gas industry that need to make bets on how active the coming hurricane season will be. Unfortunately, the CSU June 1 forecasts do poorly at forecasting the number of major hurricanes (only 3% skill), and major hurricanes cause 80% - 85% of all hurricane damage (normalized to current population and wealth levels). This year's June forecast uses a new formula tried in 2011 for the first time, so there is no way to evaluate its performance. An Excel spreadsheet of their forecast skill (expressed as a mathematical correlation coefficient) show values from 0.41 to 0.62 for their June forecasts made between 1984 and 2010, which is respectable.
TSR predicts a near-average hurricane season
The British private forecasting firm Tropical Storm Risk, Inc. (TSR) calls for 12.7 named storms, 5.7 hurricanes, 2.7 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 98, which is near average. TSR rates their skill level as 23 - 27% higher than a no-skill forecast made using climatology alone. TSR predicts a 48% chance that U.S. landfalling activity will be above average, a 26% chance it will be near average, and a 26% chance it will be below average. TSR’s two predictors for their statistical model are the forecast July-September trade wind speed over the Caribbean and tropical North Atlantic, and the forecast August-September 2012 sea surface temperatures in the tropical North Atlantic.
TSR projects that 3.6 named storms will hit the U.S., with 1.6 of these being hurricanes. The averages from the 1950-2011 climatology are 3.1 named storms and 1.5 hurricanes. They rate their skill at making these June forecasts for U.S. landfalls at 7 - 11% higher than a no-skill forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects 1.2 named storms, 0.5 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.
FSU predicts a slightly above-average hurricane season: 13 named storms
The Florida State University (FSU) Center for Ocean-Atmospheric Prediction Studies (COAPS) issued their fourth annual Atlantic hurricane season forecast, calling for a 70% probability of 10 - 16 named storms and 5 - 9 hurricanes. The mid-point forecast is for 13 named storms, 7 hurricanes, and an accumulated cyclone energy (ACE) of 122. The scientists use a numerical atmospheric model developed at COAPS to understand seasonal predictability of hurricane activity. The model is one of only a handful of numerical models in the world being used to study seasonal hurricane activity and is different from the statistical methods used by other seasonal hurricane forecasters such as Colorado State, TSR, and PSU (NOAA uses a hybrid statistical-dynamical model technique). The FSU forecast has been the best one over the past three years, for predicting numbers of Atlantic named storms and hurricanes:
2009 prediction: 8 named storms, 4 hurricanes. Actual: 9 named storms, 3 hurricanes
2010 prediction: 17 named storms, 10 hurricanes. Actual: 19 named storms, 9 hurricanes
2011 prediction: 17 named storms, 9 hurricanes. Actual: 19 named storms, 7 hurricanes
Penn State predicts a near-average hurricane season: 11 named storms
A statistical model by Penn State's Michael Mann and alumnus Michael Kozar is calling for an average Atlantic hurricane season with 11.2 named storms, plus or minus 3.3 storms. Their prediction was made using statistics of how past hurricane seasons have behaved in response to sea surface temperatures (SSTs), the El Niño/La Niña oscillation, the North Atlantic Oscillation (NAO), and other factors. The statistic model assumes that in 2012 the current 0.35°C above average temperatures in the MDR will persist throughout hurricane season, the El Niño phase will be neutral to slightly warm, and the North Atlantic Oscillation (NAO) will be near average. The PSU team has been making Atlantic hurricane season forecasts since 2007, and these predictions have been relatively accurate:
2007 prediction: 15 named storms, Actual: 15
2009 prediction: 12.5, named storms, Actual: 9
2010 prediction: 23 named storms, Actual: 19
2011 prediction: 16 named storms, Actual: 19
UK Met Office predicts a slightly below-average hurricane season: 10 named storms
The UK Met Office uses a combination of their Glosea4 model and the ECMWF system 4 model to predict seasonal hurricane activity. These dynamical numerical models are predicting a slightly below-average season, with 10 named storms and an ACE index of 90. 
NOAA predicts an average hurricane season: 12 named storms
NOAA forecasts a near-normal Atlantic hurricane season in 2012, in their May 24 outlook. They give a 50% chance of a near-normal season, a 25% chance of an above-normal season, and a 25% chance of a below-normal season. They predict a 70% chance that there will be 9 - 15 named storms, 4 - 8 hurricanes, and 1 - 3 major hurricanes, with an Accumulated Cyclone Energy (ACE) 65% - 140% of the median. If we take the midpoint of these numbers, NOAA is calling for 12 named storms, 6 hurricanes, 2 major hurricanes, and an ACE index 102% of normal. This is very close to the 1981 - 2010 average of 12 named storms, 6 hurricanes, and 3 major hurricanes. Hurricane seasons during the active hurricane period 1995 - 2011 have averaged 15 named storms, 8 hurricanes, and 4 major hurricanes, with an ACE index 153% of the median. Only five seasons since 1995 have not been above normal—including four El Niño years (1997, 2002, 2006, and 2009), and the neutral 2007 season.
How accurate are the NOAA seasonal hurricane forecasts?
Over the past twelve years, a forecast made using climatology was in error, on average, by 3.6 named storms, 2.5 hurricanes, and 1.7 intense hurricanes. NOAA's May forecast was not significantly better than climatology for these quantities, with average errors of 3.5 named storms, 2.3 hurricanes, and 1.4 intense hurricanes. Only NOAA's May ACE forecast was significantly better than climatology, averaging 58 ACE units off, compared to the 74 for climatology. Using another way to measure skill, the Mean Squared Error, May NOAA forecasts for named storms, hurricanes, and intense hurricanes had a skill of between 5% and 21% over a climatology forecast. Not surprisingly, NOAA's August forecasts were much better than the May forecasts, and did significantly better than a climatology forecast.
NOAA predicts an average Eastern Pacific hurricane season
NOAA's pre-season prediction for the Eastern Pacific hurricane season, issued on May 24, calls for a near-average season, with 12 -18 named storms, 5 - 9 hurricanes, 2 - 5 major hurricanes, and an ACE index 70% - 130% of the median. The mid-point of these ranges gives us a forecast for 15 named storms, 7 hurricanes, and 3.5 major hurricanes, with an ACE index exactly average. The 1981 - 2010 averages for the Eastern Pacific hurricane season are 15 named storms, 8 hurricanes, and 4 major hurricanes. So far in 2012, there have been two named storms. On average, the 2nd storm of the year doesn't form until June 25. 2012 had a record early appearance of the season's second named storm (Bud on May 21). Bud was also the strongest Eastern Pacific hurricane on record for so early in the year. Records in the Eastern Pacific extend back to 1949.
Western Pacific typhoon season forecast not available
Dr. Johnny Chan of the City University of Hong Kong issues a seasonal forecast of typhoon season in the Western Pacific, but this forecast is not yet available (as of June 2). An average typhoon season has 27 named storms and 17 typhoons. Typhoon seasons immediately following a La Niña year typically see higher levels of activity in the South China Sea, especially between months of May and July. Also, the jet stream tends to dip farther south than usual to the south of Japan, helping steer more tropical cyclones towards Japan and Korea. With the formation of Tropical Storm Mawar east of the Philippines, the Western Pacific is on the normal climatological pace for formation of the season's third storm.