North Atlantic 2022 Tropical Cyclone Season Forecast: 10th Most-active in 1950-2021 Climatology

Highlight: The 2022 forecast is projected as 10^th most active/20^th most intense in the 1950-2021 climatology. Florida is a prime target.

Executive summary: The Climate Impact Company early April North Atlantic Seasonal Tropical Cyclone Forecast for 2022 indicates 19 tropical storms, 9 hurricanes and 4 intense hurricanes are expected. The forecast ranks in the top 10 most active seasons given the 1950-2021 climatology. The accumulative cyclone energy (ACE) index forecast is 135 which ranks the intensity forecast of the 2022 season at 20^th most intense given the 1950-2021 climatology. The core of the tropical cyclone season mid-atmospheric relative humidity forecast is above normal across Florida and just-off the East Coast where coastal strikes of tropical cyclones for the 2022 season is highest. The forecast is based on a multivariate ENSO index analog which indicates weakening La Nina by mid-year followed by neutral ENSO and a warmer than normal North Atlantic basin as defined by projections of the Atlantic multi-decadal oscillation and tropical North Atlantic index.

Table 1: The Climate Impact Company 2022 North Atlantic basin seasonal tropical cyclone activity forecast compared to various climatology and the past 2 seasons.

New methodology discussion: Climate Impact Company (CIC) introduces a new methodology for forecasting tropical cyclone activity in the North Atlantic basin for the 2022 season. The forecast contains three components: 1.) Activity forecast; 2.) Intensity forecast and 3.) Location forecast.

The activity forecast is prepared differently. The conventional analog approach is to project ENSO phase based on Nino34 SSTA through the tropical cyclone season and match that projection and the 6-12 month lead-in to that pattern with other past years. Beginning this year, the activity forecast is generated differently.

A double La Nina has taken place since spring 2020. Using the conventional Nino34 SSTA to identify ENSO phase, La Nina briefly weakened to neutral phase from MAY to SEP last year before regenerating in October. However, the multivariate ENSO index (MEI) which is an atmospheric measure of the response to SSTA in the equatorial Pacific Ocean has maintained moderate-to-strong La Nina for nearly 2 consecutive years with no break. The global climate pattern has encountered 2 consecutive years of La Nina influences.

Given the well-correlated activity level of tropical cyclone activity in the North Atlantic (and all other ocean basins) to the ENSO climate, CIC identifies MEI as a more representative ENSO diagnostic. Therefore, the activity forecast for the North Atlantic basin is based on a MEI analog.

The intensity of North Atlantic basin tropical cyclone season is largely dependent on the upper ocean heat in the North Atlantic basin. The upper ocean heat is realized basin-wide by the Atlantic multi-decadal oscillation (AMO) and the tropical North Atlantic (TNA) index which covers the tropics from 5N to 23N in-between the Caribbean Sea and northwest Africa Coast. The TNA region also matches the main development region (MDR) for hurricanes.

CIC has identified that in general the most intense tropical cyclone seasons (as identified by accumulative cyclone energy [ACE index]) occur when AMO and TNA combined are in very positive (warm) phase. Projecting the AMO and TNA combined for AUG/SEP/OCT 2022 will determine the intensity of the tropical cyclone season.

Finally, an estimate of where the prevailing tropical cyclone tracks will generate and intensify can be determined by using the (ENSO + AMO/TNA) analog years to project 600 MB relative humidity (RH). The 600 MB RH is at about the halfway altitude point in the tropical/subtropical troposphere. Areas with above normal RH are likely to encounter development or passage of tropical cyclones. By combining the RH forecast and monthly climatology, a reasonably accurate projection of where tropical cyclone activity is most active on a monthly basis for the upcoming season is provided.

The climate forecast: The ENSO/tropical cyclone activity relationship for the North Atlantic basin using MEI index is updated (Fig. 1). Not surprisingly, a moderate (or stronger) La Nina is the ENSO climate regime producing the most tropical cyclones. Interestingly, weaker La Nina episodes render slightly more hurricanes than stronger La Nina regimes. Neutral ENSO distinctively averages near normal seasonal activity in-between the more active La Nina years and less active El Nino years. Previously, neutral ENSO climatology was very similar to La Nina climatology. El Nino MEI signatures are well-correlated with diminished seasonal activity.

Fig. 1: Based on multivariate ENSO index the North Atlantic tropical cyclone climatology for 1979-2021.  

The MEI analog forecast for 2022 is reasonably straight-forward. Using the 2-year La Nina climate as the starting point to identify past analogs render 4 similar regimes. Projecting the analog years forward produces a forecast indicating a weakening La Nina through June followed by neutral ENSO for the second half of 2022 (Fig. 2). The MEI-based ENSO outlook indicates the 2022 tropical cyclone season in the North Atlantic basin should average slightly above normal. The MEI-computed climatology for the North Atlantic basin indicates the 30-year normal is about 15 tropical storms. 7 hurricanes and 3 major hurricanes (Table 2).

Fig. 2: Climate Impact Company ENSO analog using multivariate ENSO index to project ENSO phase for the remainder of 2022.

Table 1: Climatology of North Atlantic basin tropical cyclone activity based on multi-variate ENSO index.

The long-term cycle of ENSO and AMO changed phase in or shortly after 1995 and remains steady since that time. The ENSO/AMO long-term cycle lasts 2-4 decades. During the similar ENSO and AMO cycle from 1995 to 2021, a total of 9 unusually intense tropical cyclone seasons (identified using ACE index) have generated. The 30-year MEI climatology indicates ACE is typically near 110 for a given season. The range of ACE index for the 9 most intense years ranges from 165 to 250. On average the AMO + TNA index for AUG/SEP/OCT for the 9 most intense years is +0.88 with 3 years >1.00. The 30-year normal of the AMO +TNA index is +0.58. The CIC analog forecast for AMO + TNA reveals a AUG/SEP/OCT value of +0.69 (Fig. 3) which represents above normal seasonal intensity but not as strong as the 9 most intense years since 1995.

Fig. 3: Climate Impact Company analog forecast of the North Atlantic basin combining Atlantic multi-decadal oscillation and tropical North Atlantic index.

Research has identified the mid-layer of the atmosphere RH as an excellent predictor of where tropical cyclones are most likely to track and intensify. During the very active period of 2016-2021 in the North Atlantic basin a total of 38 tropical cyclones have struck the U.S. coast, easily a record for a 6-year period. During that time, the RH values have been buoyant across the Gulf of Mexico and off the East Coast (Fig. 4).

Given the ENSO (2020, 2012, 2009 and 2000) and AMO +TNA (2019, 2014, 2008 and 2001) analog years the expected RH pattern for AUG/SEP/OCT 2022 indicates above normal RH and therefore presence of increased tropical cyclone risk centered on Southern Florida and just-off the U.S. East Coast (Fig. 5). Combining monthly climatology and the above normal RH zones, significant tropical cyclones are likely to follow two paths in August: Into the Louisiana Coast and especially just-off the U.S. East Coast. In September, the primary tropical cyclone tracks are out of the central North Atlantic tropics and toward Florida with either a Florida strike and then into the Gulf of Mexico or a north to northeast veering and staying off the U.S. East Coast. In October, there is an above normal risk of a southwest Caribbean Sea tropical cyclone moving north-northeast across Florida. The RH-based analog forecast implicates Florida as a primary U.S. tropical cyclone target during the core of the 2022 season.

Fig. 4: During AUG/SEP/OCT of 2016 to 2021 the 600 MB RH has averaged much above normal in the Gulf of Mexico and just-off the U.S. East Coast. During this 6-year period an unprecedented 38 tropical cyclones have struck the U.S. coast.

Fig. 5: Based on the ENSO and AMO/TNA analogs, the RH anomaly projection for AUG/SEP/OCT 2022 combined with monthly climatology renders the primary tropical cyclone tracks indicated.

The seasonal activity forecast: The analog years used to project the environment across the North Atlantic basin are 2020, 2012, 2009 and 2000 for ENSO and 2019, 2014, 2008 and 2001 for AUG/SEP/OCT AMO +TNA. Due to unusual upper-level shear across the North Atlantic basin likely related to the Mount Redoubt Alaska Volcano in 2009 and upper trough across a large cool pool of water that developed in the mid-North Atlantic basin in 2014 these analog years are omitted from the seasonal tropical cyclone activity calculation for 2022 (Table 2). The forecast is 19 tropical storms, 9 hurricanes and 4 intense hurricanes. Once again, the seasonal activity expected for 2022 is above the MEI 15-year and 30-year climatology and in the top ten most active years given the 1950-2021 TC climatology. The ACE index forecast is 135 which ranks the 2022 season as 20^th most intense in the 1950-2021 climatology.

Table 2: CIC seasonal activity forecast for the 2022 North Atlantic basin tropical cyclone season.

Other climate factors: The quasi-biennial oscillation (QBO) has shifted into negative phase which likely peaks mid-year and begins to weaken during the peak of the tropical cyclone season. When -QBO is present, ventilation in the deep tropics which enhances tropical cyclone development is suppressed. However, in the subtropics upper-level ventilation is enhanced. Consequently, the 2022 tropical cyclone season is likely to feature strongest activity in the subtropics. The RH forecast is well-correlated to the QBO outlook for AUG/SEP/OCT 2022 indicating above normal RH in the subtropics while the mid-atmosphere is drier than normal in the deep tropics. Tropical cyclone activity in the North Atlantic basin is generally above normal when the tropical Africa climate is wet. In this wet zone tropical waves generated are stronger than normal once entering the North Atlantic basin and more capable of becoming tropical cyclones. This regime is expected for the upcoming season. Finally, presence of Madden Julian oscillation (MJO) extending across the tropical North Atlantic basin and tropical Africa enhances tropical cyclone activity. MJO projections in April for upcoming TC season are not possible. However, once into the TC season the MJO pattern becomes the top predictor of when TC activity increases.

Forecast summary: The Climate Impact Company 2022 North Atlantic tropical cyclone season forecast is based on a new forecast methodology. The methodology accounts for activity, intensity and location. The activity forecast indicates 19 tropical storms, 9 hurricanes and 4 intense hurricanes for the 2022 season. The activity forecast rank is in the top ten highest from the 1950-2021 climatology. The ACE index forecast which identifies the intensity of the season is 135 ranking 20^th most intense in the 1950-2021 climatology. The location forecast favors the most active and intense zone for tropical cyclones across Florida and just-off the U.S. East Coast. Florida is primary landfall target for 2022 tropical cyclones. The forecast is based on a multivariate ENSO index analog combined with analogs for the North Atlantic SSTA pattern by combining both the AMO and TNA regimes.

Other forecasts: Seasonal forecasts issued by Colorado State University (later today), Tropical Storm Risk U.K. (April 12^th) and NOAA (May) will be compared with the CIC forecast once available.

Forecast verification: Climate Impact Company has issued seasonal forecasts for North Atlantic tropical cyclones since 2004 and the methodology was used at a major U.S. weather company from 1999-2003. The early seasonal forecasts, issued in April compared with observed results indicate reasonably accurate projections (grade of A or B) in 16 of 22 years with 3 years when the early forecast failed (Table 3).

Table 3: Climate Impact Company North Atlantic basin pre-seasonal forecasts compared to observed and the attendant error. Red = El Nino year.