NOAA Predicts a Quiet Atlantic Hurricane Season: 8 - 13 Named Storms

The Atlantic hurricane season starts in just over a week, and long-range models are already pointing to the possibility that the Western Caribbean will be capable of brewing the season's first "Invest" during the first week of June. But so far, the major hurricane forecasting groups are not impressed with this season's potential to be an active one. They are calling for 2014 to be a below average to near-average year for the Atlantic. NOAA's prediction, issued this Thursday morning, forecasts a 50% chance of a below-normal season, a 40% chance of an near-normal season, and only a 10% chance of an above-normal season. They predict a 70% chance that there will be 8 - 13 named storms, 3 - 6 hurricanes, and 1 - 2 major hurricanes, with an Accumulated Cyclone Energy (ACE) 40% - 100% of the median. If we take the midpoint of these numbers, NOAA is calling for 10.5 named storms, 4.5 hurricanes, 1.5 major hurricanes, and an ACE index 70% of normal. This is below the 1981 - 2010 average of 12 named storms, 6 hurricanes, and 3 major hurricanes. Hurricane seasons during the active hurricane period 1995 - 2013 have averaged 15 named storms, 8 hurricanes, and 4 major hurricanes, with an ACE index 151% of the median.



NOAA cites three key factors influencing their forecast for a below-normal to near-normal hurricane season:

1) An El Niño event is predicted for the summer and fall, which is expected to bring strong wind shear-inducing upper-level winds over the Tropical Atlantic. Vertical wind shear during the past 30 days was stronger than average across much of the Main Development Region (MDR) for hurricanes, from the coast of Africa to the Caribbean. Sinking air at mid-and upper-levels was also stronger than average. The development of El Niño would mean a likely continuation of these non-conducive conditions, and both versions of NOAA's long-range CFS model are predicting enhanced vertical wind shear across the western MDR during August-September-October 2014. Strong vertical wind shear and sinking motion, linked to a rare jet stream pattern of record strength, were key suppressing factors during the unexpectedly quiet 2013 Atlantic hurricane season.

2) Sea Surface Temperatures (SSTs) are near average in the MDR. Many long-range dynamical computer forecast models are predicting that SSTs in the MDR will remain near- or below-average throughout the hurricane season.

3) We are in an active hurricane period that began in 1995, and this positive phase of the Atlantic Multi-decadal Oscillation (AMO) may act to keep hurricane activity higher than it would otherwise be.

Colorado State predicts a below-average hurricane season: 10 named storms
A below-average Atlantic hurricane season is on tap for 2014, according to the June 2 seasonal hurricane forecast by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team is calling for 10 named storms, 4 hurricanes, and 1 intense hurricane, and an Accumulated Cyclone Energy (ACE) of 65, about 2/3 of average. The forecast calls for a below-average chance of a major hurricane hitting the U.S., both along the East Coast (22% chance, 31% chance is average) and the Gulf Coast (23% chance, 30% chance is average). The risk of a major hurricane in the Caribbean is also below average, at 32% (42% is average.)

Figure 1. Category 4 Hurricane Lili in the Gulf of Mexico at 16:45 UTC on October 02, 2002. Lili was the strongest hurricane of 2002, a year that the Colorado State seasonal forecast team lists as an analogue for 2014. Lili weakened to a Category 1 storm before hitting Louisiana, causing just under $1 billion in damage.

CSU's Analogue years: 2009, 2002, 1997, 1965, and 1957
The CSU team picked five previous years when atmospheric and oceanic conditions were similar to what they expect for this year: at least moderate El Niño conditions, neutral to slightly cool sea surface temperatures in the tropical Atlantic, and a positive phase of the Atlantic Multi-decadal Oscillation (AMO). Those five years were 2009, a quiet year with 9 named storms, 3 hurricanes, and 2 major hurricanes; 2002, which featured two major hurricanes that got their names retired: Lili and Isidore; 1997, a quiet year with only 8 named storms and 3 hurricanes; 1963, with 9 named storms and 7 hurricanes, including Cuba's deadliest hurricane of all-time: Hurricane Flora (8,000 killed); and 1957, a below-average year with 8 named storms and 2 major hurricanes, including June's deadly Hurricane Audrey, which was re-analyzed as a Category 3 storm this year. The average activity during these five analogue years was 9 named storms, 4 hurricanes, and 2 major hurricanes. The CSU team will issue an updated forecast on July 31, 2014.


Figure 2. Comparison of the percent improvement in mean square error over climatology for seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 2004-2013, using the Mean Square Skill Score (MSSS). The figure shows the results using two different climatologies: a fixed 50-year (1950 - 1999) climatology, and a 2004 - 2013 climatology. Skill is poor for forecasts issued in December and April, modest for June forecasts, and good for August forecasts. Image credit: Tropical Storm Risk, Inc.

TSR predicts a near-average hurricane season: 12 named storms
The April 7 forecast for the 2014 Atlantic hurricane season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) calls for a near-average season with 12 named storms, 5 hurricanes, 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 75. The long-term averages for the past 64 years are 11 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE of 102. TSR rates their skill level as modest for these April forecasts: 7 - 15% higher than a "no-skill" forecast made using climatology. They project that 3 named storms will hit the U.S., with 1 of these being a hurricane. The averages from the 1950-2013 climatology are 3 named storms and 1 hurricane hitting the United States. TSR rates their skill at making these April forecasts for U.S. landfalls just 5% - 8% higher than a "no-skill" forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects one named storm and no hurricanes in 2014. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR's two predictors for their statistical model are the forecast July - September trade wind speeds over the Caribbean and tropical North Atlantic, and the forecast August - September 2013 sea surface temperatures (SSTs) in the tropical North Atlantic Main Development Region (MDR) for hurricanes. Their model is calling for SSTs 0.32°C below average and trade winds 1 m/s stronger than average during these periods; both of these factors should act to decrease hurricane and tropical storm activity. The July-September 2014 trade wind prediction is based on an expectation of moderate El Niño conditions in August-September 2014. TSR will issue an updated forecast on May 27, 2014.

Penn State predicts a below-average hurricane season: 9 named storms
A statistical model by Penn State's Michael Mann, alumnus Michael Kozar, and researcher Sonya Miller is calling for a quiet Atlantic hurricane season with 9.3 named storms, plus or minus 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 statistical model assumes that the mid-May 2014 0.29°C above average SSTs in the MDR will persist throughout hurricane season, a moderate El Niño will be in place, 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 done pretty well, except for in 2012, when an expected El Niño did not materialize. They were the only major forecast group that issued a successful 2013 Atlantic hurricane season forecast.

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
2012 prediction: 10.5 named storms, Actual: 19
2013 prediction: 16 named storms, Actual: 14

FSU predicts a below-average hurricane season: 7 named storms
The Florida State University (FSU) Center for Ocean-Atmospheric Prediction Studies (COAPS) issued their sixth annual Atlantic hurricane season forecast on May 29, and went the lowest of any of the major forecast group: a 70% probability of 5 - 9 named storms and 2 - 6 hurricanes. The mid-point forecast is for 7 named storms, 4 hurricanes, and an accumulated cyclone energy (ACE) of 60. 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 did well in 2009 - 2012, but badly missed the number of hurricanes in their 2013 prediction (8 predicted, but only 2 formed):

2009 prediction: 8 named storms, 4 hurricanes. Actual: 9 named storms, 3 hurricanes
2010 prediction: 17 named storms, 10 hurricanes. Actual: 19 named storms, 12 hurricanes
2011 prediction: 17 named storms, 9 hurricanes. Actual: 19 named storms, 7 hurricanes
2012 prediction: 13 named storms, 7 hurricanes. Actual: 19 named storms, 10 hurricanes
2013 prediction: 15 named storms, 8 hurricanes. Actual: 14 named storms, 2 hurricanes

UK Met Office predicts a below-average hurricane season: 10 named storms
The UKMET office forecast for the 2014 Atlantic hurricane season, issued May 16, calls for below-average activity, with 10 named storms, 6 hurricanes, and an ACE index of 84. In contrast to the statistical models relied upon by CSU, TSR, PSU, and NOAA, the UKMET forecast is done strictly using two dynamical global seasonal prediction systems: the Met Office GloSea5 system and ECMWF system 4. Their forecasts for the past two years have not verified well:

2012 prediction: 10 named storms, ACE index of 90; Actual: 19 named storms, ACE index of 123
2013 prediction: 14 named storms, 9 hurricanes, ACE index of 130; Actual: 14 named storms, 2 hurricanes, ACE index of 31

Predictions from WU, WSI, and NC State
Weather Underground Community Hurricane Forecast: 12 named storms, 5 hurricanes, 2 major hurricanes
WSI: 11 named storms, 5 hurricanes, 2 major hurricanes
North Carolina State: 9.5 named storms, 5 hurricanes, 2 major hurricanes

NOAA predicts an above-normal or near-normal Eastern Pacific hurricane season: 17 named storms
As is usually the case when an El Niño event is threatening, NOAA's pre-season prediction for the Eastern Pacific hurricane season, issued on May 22, is calling for an active season. NOAA expects there to be 14 - 20 named storms, 7 - 11 hurricanes, 3 - 6 major hurricanes, and an ACE index 95% - 160% of the median. The mid-point of these ranges gives us a forecast for 17 named storms, 9 hurricanes, and 4.5 major hurricanes, with an ACE index 127.5% of average. The 1981 - 2010 averages for the Eastern Pacific hurricane season are 15 named storms, 8 hurricanes, and 4 major hurricanes. The outlook calls for a 50% chance of an above-normal season, a 40% chance of a near-normal season, and a 10% chance of a below-normal season. El Niño decreases the vertical wind shear over the tropical Eastern Pacific, favoring the development of more and stronger tropical cyclones. Since 1995 the Eastern Pacific has been in an era of low activity for hurricanes, but this pattern will be offset in 2014 by the impacts of El Niño.

NOAA predicts a near-normal or above-normal Central Pacific hurricane season
NOAA's pre-season prediction for the Central Pacific hurricane season, issued on May 22, calls for a near-normal or above-normal season, with 4 -7 tropical cyclones. An average season has 4 - 5 tropical cyclones, which include tropical depressions, tropical storms, and hurricanes. The outlook calls for a 40% chance of a near-normal season, a 40% chance of an above-normal season, and a 20% chance of a below-normal season. El Niño decreases the vertical wind shear over the tropical central Pacific, favoring the development of more and stronger tropical cyclones. Since 1995 the central Pacific has been in an era of low activity for hurricanes, but this pattern will be offset in 2014 by the impacts of El Niño. Hawaii is the primary land area affected by Central Pacific tropical cyclones.

Even a quiet hurricane season can be devastating
Quiet hurricane seasons with below-average activity can still produce major hurricanes that cause massive devastation. The five seasons that CSU lists as analogue years for 2014 produced five hurricanes that had their names retired, including one that killed 8,000 people in Cuba (Flora of 1963) and one that killed over 400 people in Texas and Louisiana (Audrey of 1957.) Even if an El Niño does develop this year, that doesn't mean it will be a quiet season. Recall the El Niño year of 2004, when four major hurricanes pounded the U.S.--Ivan, Charlie, Jeanne, and Frances. Those of you in Hurricane Alley should prepare for the 2014 season the same way you would for a predicted hyperactive season, and be ready for the Storm of the Century to hit your location.

Jeff Masters