SEASONAL PREDICTION OF SEASONAL PREDICTION OF HURRICANE ACTIVITY REACHING HURRICANE ACTIVITY REACHING

THE COAST OF THE UNITED THE COAST OF THE UNITED STATESSTATES

Mark Saunders and Adam LeaMark Saunders and Adam Lea

Department of Space and Climate PhysicsDepartment of Space and Climate PhysicsUniversity College LondonUniversity College London

RMS Conference 2005RMS Conference 2005Exeter UniversityExeter University

16 September 200516 September 2005

Tropical Storm Risk (TSR)Tropical Storm Risk (TSR)

Founded in 2000, Founded in 2000, Tropical Storm Risk (TSR)Tropical Storm Risk (TSR) offers a offers a leading resource for forecasting the risk from tropical leading resource for forecasting the risk from tropical storms worldwide. storms worldwide.

The current TSR consortium comprises experts on The current TSR consortium comprises experts on insurance, risk management and seasonal climate insurance, risk management and seasonal climate forecasting.forecasting.

Industry partners: Industry partners: Benfield, Royal &SunAlliance, Benfield, Royal &SunAlliance, Crawford & CompanyCrawford & Company. .

Scientific partner:Scientific partner: UCL/BenfieldhrcUCL/Benfieldhrc. .

US Hurricane ImpactsUS Hurricane Impacts

Annual total (economic) Annual total (economic) and insured losses and insured losses 1950-2004 from 1950-2004 from hurricanes striking the hurricanes striking the U.S.U.S. are estimated to be are estimated to be US $ 5.6 bn and US $ US $ 5.6 bn and US $ 3.0 bn3.0 bn respectively at respectively at 2004 prices and 2004 prices and exposures.exposures.

Hurricane KatrinaHurricane Katrina11:00 UT 29 August 200511:00 UT 29 August 2005

(Courtesy NOAA)(Courtesy NOAA)

Seasonal Forecast RelevanceSeasonal Forecast Relevance

• Strong correlation link (Strong correlation link (0.68; 1900-20040.68; 1900-2004) exists ) exists between U.S. hurricane activity and loss.between U.S. hurricane activity and loss.

• Skillful seasonal forecasts of Skillful seasonal forecasts of U.S. landfalling U.S. landfalling hurricane activityhurricane activity would benefit society, would benefit society, business and government by business and government by reducing risk, reducing risk, uncertainty and financial volatilityuncertainty and financial volatility..

• However, significant seasonal U.S. landfalling However, significant seasonal U.S. landfalling skill has not been shown to date. skill has not been shown to date.

What We Have DoneWhat We Have Done

• We show that seasonal US landfalling hurricane wind We show that seasonal US landfalling hurricane wind energy 1950-2003 is predictable from theenergy 1950-2003 is predictable from the 1 August 1 August start of the main Atlantic hurricane season withstart of the main Atlantic hurricane season with useful and significantuseful and significant ( (rrrankrank = 0.67; = 0.67; pp < 0.001) < 0.001) skill.skill.

• Predictability arises from tropospheric height-Predictability arises from tropospheric height-averaged wind anomalies present over the North averaged wind anomalies present over the North Atlantic, North America and east Pacific during July Atlantic, North America and east Pacific during July which which establishes persistent steering winds that establishes persistent steering winds that either favour or hinder US hurricane landfalleither favour or hinder US hurricane landfall. .

• Hindcasts are linked significantly (Hindcasts are linked significantly (rrrankrank = 0.48; = 0.48; pp < <

0.010.01) to U.S. hurricane economic and insured losses ) to U.S. hurricane economic and insured losses 1950-2003. 1950-2003.

Monthly Distribution of U.S. Monthly Distribution of U.S. Hurricane StrikesHurricane Strikes

97% of intense (Cat 3 to 5) hurricane strikes on the U.S. and 97% of intense (Cat 3 to 5) hurricane strikes on the U.S. and 87% of hurricane hits on the U.S. occur after 1 August. 87% of hurricane hits on the U.S. occur after 1 August.

(1950-2004 Data)

DataData

• Use the NOAA Use the NOAA Accumulated Cyclone Energy Accumulated Cyclone Energy (ACE) index(ACE) index as our measure of landfalling as our measure of landfalling hurricane wind energy and define this as the hurricane wind energy and define this as the US ACE indexUS ACE index. .

• U.S. National Hurricane Center’s North Atlantic U.S. National Hurricane Center’s North Atlantic hurricane database. hurricane database.

• Monthly gridded wind data Monthly gridded wind data averaged between averaged between 925 and 400 mb925 and 400 mb from the NCEP/NCAR global from the NCEP/NCAR global reanalysis project 1950-2003.reanalysis project 1950-2003.

• U.S. hurricane economic and insured loss data U.S. hurricane economic and insured loss data are obtained from are obtained from Pielke and Landsea (1998)Pielke and Landsea (1998) and from and from Collins and Lowe (2000)Collins and Lowe (2000) respectively. respectively.

Height-Averaged Winds and Height-Averaged Winds and US ACE Index US ACE Index

Figure shows height-averaged wind anomalies in Figure shows height-averaged wind anomalies in (a)(a) July July and and (b)(b) August-September-October linked significantly August-September-October linked significantly to years of above-median US ACE index 1950-2003. to years of above-median US ACE index 1950-2003.

Hindcast Skill for US ACE IndexHindcast Skill for US ACE Index

Comparison Comparison of strength, of strength,

significance significance and stationarity and stationarity

in skill from in skill from three models.three models.

Hindcast skill Hindcast skill is significant to is significant to

pp = 0.001 over = 0.001 over each of the sub-each of the sub-

periods 1950-1976 periods 1950-1976 and 1977-2003.and 1977-2003.

Hindcast Skill ComparisonHindcast Skill Comparison

Hindcast skill from Hindcast skill from the July wind the July wind

model is model is doubledouble that possible from that possible from

knowing the knowing the observed North observed North

Atlantic total ACEAtlantic total ACE index at the index at the

hurricane season hurricane season end on 30th end on 30th November.November.

Hindcast Link to Losses (1)Hindcast Link to Losses (1)

Link between hindcast US ACE index and U.S. hurricane Link between hindcast US ACE index and U.S. hurricane economic and insured losses 1950-2003. economic and insured losses 1950-2003.

Real-Time PerformanceReal-Time Performance

The July 925-400mb wind index model performed well The July 925-400mb wind index model performed well in real-time operation in 2004 and 2005.in real-time operation in 2004 and 2005.

20042004 US ACE Index forecast (US ACE Index forecast (4th August, 20044th August, 2004) to be in ) to be in

upper quartileupper quartile.. US hurricane losses estimated to be US hurricane losses estimated to be US $ 45 bnUS $ 45 bn

(economic) and US $ 23 bn (insured).(economic) and US $ 23 bn (insured).

20052005 US ACE Index forecast (US ACE Index forecast (5th August, 20055th August, 2005) to be in ) to be in

upper decileupper decile.. Insured losses from hurricane Katrina estimated to be Insured losses from hurricane Katrina estimated to be

US $ 40bn to US $ 60bnUS $ 40bn to US $ 60bn..

Business ApplicationBusiness ApplicationUS hurricane US hurricane total insured total insured loss contingent loss contingent on the TSR 1st on the TSR 1st August forecast.August forecast.

The chance of a The chance of a large total loss large total loss is much higher is much higher in those years in those years when the when the forecast is high.forecast is high.

SummarySummary

Further Information:Further Information:

Saunders, M. A. and A. S. Lea, Seasonal Saunders, M. A. and A. S. Lea, Seasonal prediction of hurricane activity reaching prediction of hurricane activity reaching the coast of the United States, the coast of the United States, NatureNature, , 434, 1005-1008, 2005.434, 1005-1008, 2005.

• To our knowledge this is the To our knowledge this is the first example of useful first example of useful skill for predicting seasonal US landfalling hurricane skill for predicting seasonal US landfalling hurricane activity and damage.activity and damage.

• The model has a The model has a sound physical basissound physical basis. . • The model will benefit risk awareness and offers The model will benefit risk awareness and offers

good potential for good potential for application in business decision application in business decision makingmaking. .