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01/15/2019, 10:50 am EST

North Atlantic Basin 2019 Tropical Cyclone Season Forecast (Short Version)

Executive summary: Since 2005 Climate Impact Company has issued an early season assessment of the following North Atlantic tropical cyclone season activity forecast. In 2019 the outlook indicates 14 tropical storms, 8 hurricanes and 3 intense hurricanes are expected. The activity forecast is at or slightly above both the 20-year and 30-year normal. The accumulated cyclone energy forecast is 99 which is slightly below climatology. The forecast is made with below average forecast confidence due to uncertainty in the lead predictors: El Nino southern oscillation (ENSO) and Atlantic multi-decadal oscillation (AMO). The preliminary forecast indicates both the Gulf of Mexico and East Coast are susceptible to coastal strikes of hurricanes in 2019. The next seasonal assessment will be issued in early April. Analog forecast: The preliminary Climate Impact Company 2019 North Atlantic basin tropical cyclone season forecast is based on the ENSO analog. The 2007 and 2010 analogs are weighted twice given their presence in the modern-day climate regime featuring similar long-term ENSO/PDO and AMO cycles plus the new fast-rising CO2 atmosphere. There is a lot of variance in the ENSO regimes for the analog years. If the weak El Nino forecast for the 2019 tropical cyclone season is stronger the seasonal forecast amount will be lower. If El Nino ends and is followed by La Nina the seasonal activity will be higher than forecast. The weighted average of the analog years indicates 14 tropical storms, 8 hurricanes and 3 intense hurricanes are likely across the North Atlantic basin in 2019 (Table 1). The activity forecast is similar to the 30-year and 20-year climatology although the accumulated cyclone energy index is moderately lower than climatology. The activity forecast is similar to last year and not quite as active as 2017 while ACE index is markedly lower than the past 2 years. Tropical Storms Hurricanes Intense Hurricanes ACE Index 2010 (2) 19 12 5 165 2007 (2) 15 6 2 72 1987 (1) 7 3 1 34 1977 (1) 6 5 1 25 1969 (1) 18 12 5 158 Forecast 14.1 (14) 8.0 (8) 3.0 (3) 98.71 (99) 30-year cli 13.6 7.0 3.0 115.7 20-year cli 15.0 7.4 3.4 122.4 Last Year 15 8 2 129 2 Years Ago 17 10 6 226 Table 1: Analog calculation for the 2019 North Atlantic basin tropical cyclone activity forecast. The CIC analog forecast indicates slightly higher seasonal activity compared to the Tropical Storm Risk/U.K. outlook. TSR cites a potential stronger El Nino signal holding seasonal activity too slightly below the long-term average.  The Colorado State University Tropical Prediction Project has not issued an early season forecast. CSU also cites uncertainty in the ENSO forecast and adds that the lead predictor, North Atlantic ocean temperatures as defined by the Atlantic multi-decadal oscillation may be changing phase from the warm cycle which started in the late 1990’s and has been persistent through 2014 to a cooler (or less warm) signature. A cooler North Atlantic would also hold down seasonal activity. Tropical Cyclones Hurricanes Intense Hurricanes Accumulated Cyclone Energy CIC 14 8 3 99 TSR 12 5 2 82 Last Year 15 8 2 129 30-Yr Normal 13.6 7.0 3.0 114.8 Table 2: A collection of preliminary operational forecasts of seasonal tropical cyclone activity across the North Atlantic basin in 2019. Forecast tracks: The outlook is made with below normal confidence and is susceptible to significant change when updated the first week of April. To depict the possible variance in seasonal activity for 2019 a look at the extreme upper and lower limit activity (and tracks) from the analogs is provided (Fig. 1-2). If the tropical North Atlantic is warmer than normal and ENSO is neutral to borderline El Nino (which is forecast by CIC) the season will be very active featuring up to 12 hurricanes including a very busy year in the Gulf of Mexico. Whether the tropical North Atlantic is warm enough to support this forecast (or not) is a big question mark. If El Nino is stronger (as most dynamic models indicate) and the recent trend of a cooler North Atlantic holds the seasonal activity would be minimal. Fig. 1: The “most active” scenario for 2019 based on analog years would be similar to 1969. If ENSO is near neutral or even weak El Nino (as forecast by CIC) and the tropical North Atlantic is warmer than normal (uncertain right now) the season will be very active. Fig. 2: The “least active” scenario for 2019 based on analog years would be similar to 1987. If El Nino is stronger this solution is most correct.