The 2014 Atlantic Hurricane Season Begins

The 2014 Atlantic hurricane season is officially underway, and we already have an area of interest in the Gulf of Mexico to talk about. An area of low pressure over the Southern Gulf of Mexico's Bay of Campeche is generating disorganized heavy thunderstorm activity, and this area has a slight potential to develop late this week. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave the disturbance a 10% chance of developing by Saturday. The chances for this disturbance to develop depend heavily on the fate of an area of disturbed weather in the Eastern Pacific located a few hundred miles south of Southeast Mexico (Invest 93E), which will move slowly northwards towards the Gulf of Mexico this week. Satellite loops show a steady increase in the intensity and organization of the heavy thunderstorms associated with 93E, and the system is already bringing heavy rains to Southern Guatemala and Southeast Mexico. With the 8 am EDT Monday run of the SHIPS model showing light wind shear of 5 - 10 knots and warm ocean temperatures of 29.5°C for the remainder of the week along 93E's path, development into a tropical depression is likely. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave this system an 80% chance of developing into a tropical depression or tropical storm by Wednesday, and a 90% chance by Saturday. The 06Z Monday run of the GFS model predicts that this disturbance will make landfall in Southeast Mexico on Wednesday. The 00Z Monday European model is slower, predicting a Thursday landfall. It is possible that moisture and spin from 93E will aid the spin-up of a system over the Southern Gulf of Mexico late this week. In any case, residents of Southeast Mexico and Western Guatemala appear at risk to undergo a multi-day period of very heavy rainfall likely to cause flash flooding and dangerous mudslides.


Figure 1. Latest satellite image of Invest 93.

Summary of the 2014 Atlantic hurricane season forecasts
The major hurricane forecasting groups are not impressed with this season's potential to be an active one, and are calling for 2014 to be a below average to near-average year for the Atlantic. The most daring forecast was issued by Florida State, which calls for just 7 named storms and 4 hurricanes. The other groups are calling for 9 - 12 named storms. The main reason for the quiet forecasts is the likely emergence of El Niño. Every 3 - 7 years, variations in tropical winds and pressure shift warm ocean waters eastwards from the Western Pacific to the South American coast, causing an El Niño event. The unusually warm water tends to drive an atmospheric circulation that brings strong upper-level winds to the tropical Atlantic, creating high levels of wind shear that tend to tear hurricanes apart. Another factor leading to lower forecast numbers than in previous years is the fact that sea surface temperatures in the tropical Atlantic are near average this year--quite a bit cooler than we've seen during the typical year during our active hurricane period that began in 1995.


Figure 2. Departure of sea surface temperature (SST) from average for May 29, 2014. SSTs were near average over the Atlantic Main Development Region (MDR) for hurricanes, from the coast of Africa to Central America between 10°N and 20°N, including the Caribbean. As of June 2, 2014, SSTs over the region typically used to define El Niño events, 5°N - 5°S to 120°W - 170°W (the Niño 3.4 region) were at the threshold for El Niño conditions, +0.6°C from average, according to the latest weekly NOAA El Niño update. Image credit: NOAA/NESDIS.


Figure 3. Surface winds in the Atlantic Main Development Region (MDR) for hurricanes, from the coast of Africa to Central America between 10°N and 20°N, including the Caribbean, were stronger than average during the first four months of 2014. These winds stirred up more cooler water from the depths than usual, resulting in cooler sea surface temperatures than otherwise would have occurred. The stronger trade winds were due to a persistent positive phase of the North Atlantic Oscillation (NAO), which strengthened the semi-permanent high pressure system that lies over the Azores Islands, creating a stronger clockwise flow of air around the high. Image credit: NOAA/ESRL.

NOAA predicts a below-average hurricane season: 10.5 named storms
NOAA's May 22 Atlantic hurricane season forecast predicts 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.)

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 4. 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 May 27 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

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 four 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