2021 Atlantic Hurricane Forecast Inside This Outlook 2020 Tropical Review 2 2021 Hurricane Forecast & 2 Landfall Probabilities The Oceans & La Niña 3 Historical Analogs & 4 Forecast Guidance 2021 Atlantic Hurricane Forecast 2020 Tropical Season Review The 2020 Atlantic Hurricane Season gusty winds to parts of the Mid-At- featured a record 30 named storms, lantic into New York. Then, Isaias hit 14 hurricanes, and a record tying 7 North Carolina as a hurricane before major hurricanes. 11 storms made racing up the East Coast, bringing landfall in the United States, breaking widespread power outages, numer- the previous record of 9 set in 1916. 10 ous tornadoes, and flooding rain storms during the season underwent through New England. Power outag- “rapid intensification” at some point, es were rather long lasting in parts tying another record and keeping of New Jersey, New York and Con- coastal residents on their toes. necticut, making Isaias the costli- est hurricane in the Northeast since The U.S. Gulf Coast was extremely Radar image of Hurricane Laura making Sandy in 2012. hard hit. 5 storms made landfall as landfall in Louisiana. Via NOAA. hurricanes along the Gulf Coast, The season was prolonged, and con- with Louisiana especially impacted, Louisiana since 1856. Hurricane Hanna tinued into November, with back-to- seeing 3 hurricane landfalls (Laura, also made landfall in southern Texas, back major hurricanes (Eta and Iota) Delta, and Zeta). While not as costly while Hurricane Sally struck Alabama. striking Nicaragua only 13 days and or deadly as Katrina, Laura struck 15 miles apart. This resulted in hun- the coast with winds of 150 mph, the In the Northeast, Tropical Storm Fay dreds of fatalities and billions of dol- strongest winds in a hurricane to hit brought areas of flooding rain and lars in damage from the two storms. The 2021 Outlook A 2021 hurricane season with fewer storms than 2020 is a near certainty. While some signals point to another active 2020 Tropical Cyclone Breakdown season, they are more mixed than last year. We’re leaning Named Major towards a more active than normal season, which would Period Hurricane be the sixth in a row if it verifies. Note that the “average” Storms Hurricanes numbers for named storms and hurricanes are a bit higher Thru July 2 - 4 0 - 1 0 for this season, reflecting the new 30 year averages from 1991 - 2020. Regardless, we expect a few storms in June Aug - Sept 6 - 9 3 - 6 1 - 2 and July, though most of these will tend to be weaker. A Oct - Nov 3 - 5 2 - 3 0 - 1 fairly sharp peak in activity is favored later in August into September. Many recent seasons have been slow to end, Total 13 - 17 6 - 10 2 - 3 with notable activity into at least October, and we expect (Hist. Avg) (14) (7) (3) a similar trend this year. 2021 Strike Probability Compared to Climatology With a lean towards another active season and a pattern that may steer storms towards the Mid-Atlantic at times, the risk for a tropical impact is a category higher than nor- mal from New Jersey and points south. This situation will be more likely during the first half of the season (through August). Further north, the risk of an impact is near normal for New England and Long Island. In September and early October, the threat area may shift towards the Southeast and Gulf Coast. As we saw with Isaias last year, even one direct hit can be quite damaging, and indirect impacts can still result in heavy rain and rough surf from storms pass- ing hundreds of miles away. Page 2 www.weatherworksinc.com 2021 Atlantic Hurricane Forecast The Oceans and La Niña La Niña Weakening Looking East into the Indian Ocean La Niña conditions, or cooler than usual waters across For the second year the Tropical Pacific, were in place for the 2020 hur- in a row, the Indi- ricane season and contributed to the record activity an Ocean is much across the Atlantic. The La Niña event has weakened warmer than nor- quite a bit this spring, with neutral conditions favored mal, and is most ex- for much of the summer. This isn’t a strong indicator for pansive across the above or below normal activity. Also, more spread de- western part of the velops in the guidance after August; whether we break basin. This anomaly towards El Niño, or back to La Niña, may tell if the sea- does two things: 1.) son ends up closer to normal or turns active once again. A warm Indian Ocean can stave off El Niño Indian Ocean water temperature development. El Niño anomalies. Tropical Tidbits. events (the opposite of La Niña) can limit Atlantic Ocean tropical develop- ment. 2.) The warmer Indian Ocean can provide added fuel to tropical waves that move west across Africa. These can become seeds for tropical development when they enter into the Atlantic. The set-up may help fuel a few longer-track hurricanes towards the peak of the season in August and September. As a result, these Indian Ocean waters are a potential signal for another busy season. El Niño model projections, courtesy of ECMWF. Pent-Up Atlantic Ocean Warmth It’s a rather straight-forward meteorological concept: warmer waters can fuel hurricane development. So, seeing lots of “red” (above normal water temperatures) on the Atlantic sea surface temperature map raises concern for an active season. A potential saving grace is the relatively cooler waters across the tropics, which may try to keep a lid on some longer tracked, deep tropi- cal hurricanes. However, it’s not a promise these cooler waters last into the summer. Otherwise, the warmth in the subtropics (closer to the US) may favor more activ- ity than normal, and the overall warmth of the Atlantic Atlantic Ocean water temperature anomalies. basin is enough to raise concern for increased activity. Courtesy of Tropical Tidbits. Storm Names for 2021 • Ana • Elsa • Ida • Mindy • Rose • Wanda • Bill • Fred • Julian • Nicholas • Sam • Claudette • Grace • Kate • Odette • Teresa • Danny • Henri • Larry • Peter • Victor Page 3 www.weatherworksinc.com 2021 Atlantic Hurricane Forecast Historical Analogs & Forecast Guidance A Look into the Past Because computer model fore- Last year’s analogs strongly casts become less accurate pointed to an active season; our the farther out in time we look, analogs this year are a little more we often augment the guidance mixed. As a result, they aver- by analyzing the past for long age out to a near normal season, range predictions. To do this, we with tropical activity peaking in find past years with similar cur- August and September, but con- rent and expected conditions tinuing into October. However, to this year. Then, we see how out of the four analog years from many storms occurred in these the last decade, three of them did similar seasons, and where they end up rather active, which sug- tracked. For 2021, we looked for gests we may be in a cycle where Tropical cyclone frequency for years with a weakening La Niña these conditions yield increased analogous years. in the Pacific, a warm Indian activity. Overall, the analogs sup- Ocean, a fairly warm Atlantic, along with other condi- port the idea of less activity than last season, but still tions such as upper atmospheric wind patterns. potentially finishing above normal. Favored Storm Tracks The plot to the right shows surface pressure anomalies from some of our top analog years. Blues reveal lower pres- sure than normal and the potential for increased tropical activity, where yellows indicate high pressure and reduced storminess. 2020’s analogs strongly (and correctly) favored Caribbean and Gulf Coast hurricanes, this year’s analogs are more variable. A decent signal exists for storms curv- ing well out to sea over the open Atlantic. There is also a “soft spot” from the Caribbean and Gulf of Mexico to near the East Coast, leaving the door open for some activity. It’s possible that storms curve near or just off of the East Coast during the first half of the season, then shift towards the Caribbean and Gulf of Mexico towards Sept. and Oct. Surface pressure anomalies from analog years. ESRL. Forecast Guidance Some computer guidance does run several months into the future and may provide clues for a seasonal fore- cast. However, we give these models less weight in the overall forecast due to reliability concerns at this range. Nevertheless, guidance for this season does jive with the analog and water temperature considerations discussed previously. There are some signals for an ac- tive tropical wave train coming off of Africa (note the greens), along with increased activity over the open Atlantic, especially a little farther north. There are also some signs for activity in the Gulf of Mexico and near or just off of the East Coast. Time will tell if the models Peak season rainfall anomalies from the CFS model are onto something with a dry Caribbean, suggesting (greens = wetter than normal). Tropical Tidbits. reduced activity there. Page 4 www.weatherworksinc.com.