May 2022 North Atlantic TC Seasonal Activity Forecast Update: La Nina Continues – Seasonal Activity Forecast Increases

Executive summary: The Climate Impact Company 2022 North Atlantic seasonal activity forecast has increased slightly since the initial projection one month ago. The number of tropical storms, hurricanes and intense hurricanes each increases by a count of 1 to 20 storms, 10 hurricanes and 5 intense hurricanes. The ACE index increases from 135 to 149. The increase in activity is due to a more confident La Nina climate forecast. Less confident is the extent of upper ocean heat in the tropical/subtropical North Atlantic which is forecast near average in this outlook. If the upper ocean heat forecast is warmer in subsequent updates, the number of hurricanes for 2022 will likely increase. The projected tracks for 2022 are clearly most active in the subtropics including the Gulf of Mexico, the Bahamas and close to the Southeast U.S. Coast.

Table 1: The Climate Impact Company 2022 North Atlantic basin seasonal tropical cyclone activity forecast for May 3^rd compared to the April outlook and various climatology and the past 2 seasons.

Updated climate discussion: There are important changes to the North Atlantic basin 2022 tropical cyclone seasonal activity forecast. Previously, the ENSO forecast called for a fading La Nina. Based on current conditions, their trend and adjusted dynamic model outlooks La Nina is likely to continue through the 2022 tropical cyclone season. Helping to inspire a 3^rd year in a row of La Nina climate previously not discussed is the evolution of an intense negative Indian Ocean Dipole (-IOD). The -IOD pattern helps to sustain the La Nina climate in 2022. This forecast change will increase an already buoyant activity forecast for 2022. The tropical/subtropical North Atlantic basin SSTA forecast is less confident. Forecast models disagree between near normal and warmer than normal regimes for this region. Continuation of La Nina and moderate warming of the North Atlantic tropics/subtropics supports a very active season ahead. If the North Atlantic tropics/subtropics are warmer than anticipated, a near record year could occur. Finally, a negative phase quasi-biennial oscillation (-QBO) is forecast for the upcoming season. One of the (key) -QBO analog years is 2005, the second-most active year on record. The -QBO regime suppresses deep tropics activity but enhances subtropical latitude storms. In 2005, most of massive amount of activity was located in the subtropics. The ana0log years for the 2022 forecast project very high subtropical latitude relative humidity for JUL to SEP whereas the deep tropics are quite dry which is well-correlated with the high-level atmosphere ventilation pattern associated with -QBO. Consequently, the 2022 season is likely very active in the subtropics especially the Gulf of Mexico.  

Fig. 1: Current global SSTA analysis for April 2022 reveals a resurgent La Nina, neutral IOD pattern in the tropical Indian Ocean, a somewhat suppressed “warm blob” in the North Pacific and marginal North Atlantic warmth.  

Fig. 2: The International Multi-Model Ensemble global SSTA forecast for August 2022 indicates La Nina continues, a record-strength -IOD pattern develops and helps to sustain La Nina while the near normal SSTA pattern in the North Atlantic tropics/subtropics is in-question.   

Updated seasonal activity forecast: The analog years considered approximate the ENSO, IOD, North Pacific and North Atlantic SSTA regimes forecast by the IMME model for the August. The analog years are 2001, 2010, 2016 and 2021 each weighted equally. The forecast indicates 20 tropical storms, 10 hurricanes and 5 intense hurricanes. The accumulated cyclone energy index is 149. The activity level is raised slightly from the original April 7^th outlook. The forecast maintains the busy recent 2016-21 climatology, is the 3^rd consecutive years of 20 tropical cyclones (only 4 are in the 1950-2021 climatology), the 10^th year in the 1950-2021 climatology of at least 10 hurricanes and based on ACE index tied for the 15^th most intense season. The 2022 seasonal activity forecast is considerably higher than the NEW adjusted 15-year and 30-year climatology. The 2022 season is forecast more active than last year with similar intensity.

Table 2: The Climate Impact Company seasonal activity forecast for the 2022 North Atlantic basin tropical cyclone season compared to the previous outlook and various climatology.

Fig. 3: Based on the analog years the 600 MB relative humidity projection combined with climatology identifies the most likely primary tropical cyclone tracks for the 2022 season.

Updated forecast tracks: Analog storms for the 2022 season include Hurricane Humberto (2001) which formed south of Bermuda in September and drifted northward across that small island. Another analog storm is Earl (2010) which was a major hurricane shifting out of the tropics and intensifying and just missing the U.S. East Coast. Another major hurricane in 2010 (Igor) moving north close to Bermuda is another analog storm. An early season hurricane such as Alex (2010) moving into northeast Mexico is an analog storm for 2022. Eastern Gulf of Mexico storms that turn into Western Florida are analog storms for 2022 similar to Hermine (2016). Unfortunately, Louisiana is targeted for a major hurricane in 2022 similar to the Ida track of last year. The tropical/subtropical North Atlantic 600 MB relative humidity forecast for AUG/SEP based on the analogs clearly identifies the Gulf of Mexico to Bahamas subtropics as the very active region for 2022 including the U.S. East Coast. An out-to-sea storm track across Bermuda and west of the Azores is also likely. The regime identified implies limited time to react for planning purposes. Not the dry RH pattern across and just east of the Caribbean Sea where tropical cyclone activity is suppressed. As previously stated, the prevailing RH pattern matches the anticipated -QBO pattern for the 2022 tropical cyclone season.

Other forecasts: Most forecasts are in agreement that the 2022 tropical cyclone season across the North Atlantic is more active than normal. The Climate Impact Company forecast has ticked-up a notch since the early April original outlook primarily due to the influence of a lingering La Nina episode. Anticipated is a similar slight increased with June updates of the CSU and TSR forecast. The NOAA outlook will be issued in May and should also be more active than normal.

Table 3: Lead providers of seasonal tropical cyclone activity for the North Atlantic 2022 season.

Forecast verification: The initial April seasonal activity forecasts of North Atlantic basin tropical cyclones since 1999 indicate that generally the number of tropical storms have a tendency to over-achieve the prediction most likely due to the warmer character of the ocean surface. The hurricane forecasts are generally on target except for 4 over-achieving ears in 2005, 2012, 2017 and 2021.

Fig. 4: The Climate Impact Company April seasonal forecasts and observed values for 2004 to 2021 and same forecast methodology used at DTN for 1999-2003.