2021 U.S. Hurricane Season Preview

Jeffrey Strong, Ph.D.

Combined Seasonal Forecasts

Main Factors Influencing Hurricane Activity

Sub-Seasonal Factors of Interest

Current Topics & AIR Developments

AIR Hurricane Contest

30-Yr 2020 Avg. Named 30 14 Storms

Hurricanes 14 7

Major 7 3 Hurricanes U.S. Hurricane 6 1-2 Landfalls U.S. Major Hurricane 2 <1 Landfalls

Most active season Most major hurricanes in a season

Most landfalling tropical storms Fifth consecutive above average season Most storms formed in July

Highest number of Category 4 hurricanes 27 earliest named storms Most concurrently active storms

First landfalling storm for Portugal Most storms a single storm outlasted Most storms formed before September

Most storms formed before August Strongest landfalling storm in Louisiana Most storms formed in May

Largest spread in names for currently active storms Most storms formed before October Easternmost forming storm

First time 3 storms named within 24 hours Most active September First Greek alphabet storm to make landfall in USA

Farthest north reverse extratropical transition Sixth consecutive year with pre-season storms

Rapid Intensification Hurricane Delta Strengthening to Category 4 •10 systems rapidly intensified (35+ mph in 24h) in 2020, tying record from 1995 Wind Speed Storm Time Period Increase 1 Hanna 40 mph Jul 24-25 2 Laura 65 mph Aug 25-26 3 Sally 40 mph Sep 14 4 Teddy 40 mph Sep 15-16 5 Gamma 35 mph Oct 2-3 6 Delta 85 mph Oct 5-6 7 Epsilon 50 mph Oct 20-21 8 Zeta 45 mph Oct 27-28 9 Eta 80 mph Nov 1-2 10 Iota 70 mph Nov 15-16

Consecutive Landfalls

Two instances of hurricanes making landfall within 20 • Cat 5 miles of each other • Cat 4 • Laura (Category 4 – Aug 27) & Delta (Category 2 – Oct 9) • Cat 3 near Cameron, Louisiana • Eta (Category 4 – Nov 3) & Iota (Category 4 – Nov 17) Laura • Cat 2 near Haulover, Nicaragua • Cat 1 Laura and Delta combined caused over an estimated USD 10 billion in insured property damage in the U.S. W endell Escoto/AFP via Getty Images • Laura tied the 1856 Last Island Hurricane for strongest wind speeds at landfall in Louisiana • Cat 5 Eta and Iota combined caused more than an estimated • Cat 4 USD 7 billion in damage across Central America

• Cat 3 • Iota is the strongest hurricane to make landfall in Nicaragua • Cat 2 in November on record • Cat 1

Hurricane Sally Made landfall as a Category 2 in AL September 11 – September 17 Peak Rainfall: 29.99 in – Orange Beach, AL Major to moderate flooding in many rivers

Slow forward speed allowed for heavy rainfall and widespread storm surge inundation More than 2 feet of rain logged in Alabama & Florida, with neighboring states nearing 1 foot in places

Estimated over USD 3 billion in insured property damage across U.S.

Official start of the hurricane season was June 1

Northeast Pacific North Atlantic

Tropical Storm Andres Tropical Storm Ana May 9 – May 11 May 22 – May 24 Peak Intensity: Peak Intensity: 40 mph / 1005 mb 45 mph / 1006 mb (Preliminary) (Preliminary)

NASA Eart h Observat ory

https://seasonalhurricanepredictions.bsc.es/

Named Storms Hurricanes Major Hurricanes LOW MEAN HIGH LOW MEAN HIGH LOW MEAN HIGH Forecast Average 13.6 16.9 19.7 6.3 8.2 10.3 2.4 3.8 4.8 30-Year Average 7 14 30 2 7 15 0 3 7

Ana Henri Odette

Bill Ida Peter

Claudette Julian Rose

Danny Kate Sam

Elsa Larry Teresa

Fred Mindy Victor

Grace Nicholas Wanda

©2021 AIR Worldwide CONFIDENTIAL: For Webinar Attendees Only 14 14 Seasonal Forecasts: ACE Forecast Amount of Accum. Cyclone Energy Storm Accumulated Cyclone Energy (ACE): • Storm Intensity • Storm Duration

Season ACE: Computed over each storm and depends on the frequency of occurrence of storms

ACE

LOW MEAN HIGH

Forecast Average 105.0 146.1 192.8

30-Year Average 32 122 245

©2021 AIR Worldwide CONFIDENTIAL: For Webinar Attendees Only 15 15 Seasonal Forecasts: Analog Years Potentially similar years to the upcoming hurricane season found by comparing current sea surface temperature trends & large-scale environmental trends to past hurricane seasons Top 5 Analog Years Since 1966 Top 5 Analog Years Since 1966 Based on 30-Day CDAS Global Mean Based on Tropical Pacific and Tropical Sea Surface Temperature Anomalies Atlantic Sea Surface State Named Major Named Major Year Hurricanes Year Hurricanes Storms Hurricanes Storms Hurricanes 1975 9 6 3 1996 13 9 6 2007 15 6 2 2001 15 9 4 1999 12 8 5 2008 16 8 5 2008 16 8 5 2011 19 7 4

1973 8 4 1 2017 17 10 6

30-Yr Avg. 14 7 3 30-Yr Avg. 14 7 3 Data from Tropical Tidbits Data from CSU Tropical Weather & Climate Research ©2021 AIR Worldwide CONFIDENTIAL: For Webinar Attendees Only 16 16 Main Factors Influencing Hurricane Activity

1. Warm Water

2. Vertical Instability

3. Elevated Moisture

4. Added Vorticity

5. Low Wind Shear

1. El Niño / Southern • Impacts vertical wind Oscillation (ENSO) shear and instability over Atlantic

2. Tropical Atlantic Sea • Provides energy for Surface Temperatures storms to develop and (SST) sustain convective activity

Neutral Conditions allow for above average Atlantic hurricane activity

El Niño

La Niña

ENSO Neutral conditions favored throughout the upcoming season

Average wind shear forecast across North Atlantic Main Development Region

MDR MDR

Cool Phase AMO

Warm Phase AMO

From Kaplan SST V2 per Enfield et al. (2001, GRL) Goldenberg et al. (Science, 2001)

Currently warmer than average trend in Atlantic SSTs

Jun – Jul – Aug Jul – Aug – Sep Aug – Sep – Oct Sep – Oct – Nov

NMME Models: ▪ NCEP CFSv2 ▪ CMC CanCM3 ▪ CMC CanCM4 Abnormally warm Atlantic SSTs are favored all season ▪ GFDL FLOR ▪ GFDL CM2.1 ▪ NCAR CCSM4 ▪ NASA GEOS5 ▪ NCAR CESM

• Return to neutral ENSO phase is under way

NINO 3.4 Atlantic Atlantic SSTs Wind Shear Hurricanes • Atlantic sea surface temperature remains elevated relative to average

Atlantic Atlantic SSTs Hurricanes

• Both are conducive to an ABOVE AVERAGE Atlantic Hurricane season

1. Saharan Air Layer • Impacts SST, shear, (SAL) moisture, and instability

2. Madden-Julian • Impacts instability and Oscillation (MJO) moisture

3. North Atlantic • Impacts steering Oscillation (NAO) currents

Cools Activity Surface peaks Jun–Aug Dries Mid-Levels Outbreaks every Stabilizes 3 to 5 days Air Column

Dust blowing off the Sahara Desert as seen by the NOAA-20 satellite, June 2020.

Eastward Mid-Level Dry Air Wind

Westward Wind

SAL becoming more active in Atlantic through early season

Moves eastward through the tropics for 40-60 days Enhances & suppresses instability

More active Less active

MJO staying less active in Atlantic through mid-June

NAO Negative NAO Positive Phase Phase

Modified from UCAR

Elsner (2003)

Forecast for NAO to trend neutral = More likely western Atlantic tracks

Atlantic Basin Alternate Name List Adria Heath Orlanda Braylen Isla Pax Caridad Jacobus Ronin Deshawn Kenzie Sophie Emery Lucio Tayshaun Foster Makayla Viviana Gemma Nolan Will

AMO is 40- to 60-year cycle of North Atlantic SSTs •Strong correlation between AMO Index and U.S. Major hurricane landfalls

What governs this cycle is a current area of research •Once thought to be driven internally by Atlantic Meridional Overturning Circulation •Mann et al. (2021) used output from Last Millennium Climate Reanalysis Project •Argues AMO Index is combination of periods of enhanced volcanism overlain on global climate change

AIR collaboration with the Brookings Institution and AXIS Capital Holdings Ltd.

Using AIR Hurricane Model for the United States

•Baseline catalog reflecting today’s climate •Future catalogs that reflect expected changes in frequency and severity of U.S. landfalling hurricanes Increased event frequency and sea level rise will have a meaningful impact on future damage •The growth in the number of stronger storms, and landfalling storms overall, increases modeled losses by ~20% •Loss increases extend to inland areas as stronger storms reach farther from the coast •By 2050, sea level rise may increase storm surge losses by up to 2x

Download now: https://airww.co/climateimpact

Analytics Use Cases

• Daily forecast • Understand which • Wind footprint • Select and • Estimate the order and potential areas/accounts/ Storm Development forecasts interrogate similar of magnitude for impacts locations are most 01 Up to five days prior to landfall every six hours stochastic events the event summary at risk

• View similar • Intelligently deploy • Wind footprint • Select and • Estimate range stochastic events claims resources to Pre-Landfall forecasts interrogate similar of potential to inform initial loss areas likely to be 02 48 hours prior through landfall every six hours stochastic events losses estimates daily impacted

• Custom modeled events to inform • Satellite imagery • Wind analysis • Refinement of • Identification of company and of impacted Post-Landfall footprint loss estimates impacted locations 03 3D Visual industry loss areas Intelligence estimates

30 Contest Entries Expert Forecasts 1851-2020 Climatology

0 Named Storms Hurricanes Major Hurricanes Landfalls