Caribbean/Central American Hurricane Landfall Probabilities Phil Klotzbach Department of Atmospheric Science Colorado State University Climate Diagnostics and Prediction Workshop October 27, 2009

Basic Premise: Caribbean and Central American hurricane activity is related to Atlantic basin seasonal hurricane forecasts. More active tropical cyclone seasons as predicted by the Tropical Meteorology Project (CSU) tend to have more landfalling hurricanes.

Top 10 August Hindcasts ( ) Bottom 10 August Hindcasts ( ) HURRICANE TRACKS Hurricane Days 1.75 Hurricane Days

Top 5 June Forecasts ( ) Bottom 5 June Forecasts ( ) Hurricane Days 3.25 Hurricane Days

Caribbean/Central America Probabilities Climatological and current-year probabilities of a named storm, hurricane and major hurricane within 50 miles and 100 miles of each island or landmass 50-Year Probabilities

Historical Probability Calculation Steps - Select all tropical cyclones that tracked within 50 and 100 miles of each island or landmass during the 20 th century - Assign the maximum intensity of the tropical cyclone that was reached within 50 or 100 miles of the landmass - Calculate climatological probabilities using the Poisson distribution (e.g., EP = p x /e p x!) where EP = Expected Probability p = Annual average number of tropical cyclones that have occurred in the 20 th century x = Number of storms expected in the upcoming year based on the Poisson formula - For Barbados, 26 named storms tracked within 50 miles of Barbados during the 20 th century, and therefore, the Poisson distribution gives the climatological probability of one or more named storms making landfall as 23%

50 Miles 100 Miles

Current-Year Probability Calculations - Multiply the historical number of storms that occurred over the 20 th century by predicted Net Tropical Cyclone activity (where 100% is defined to be an average season) -For example, for Barbados, if 26 named storms formed during the 20 th century and the predicted NTC was 150%, the current-year probability would be calculated based on 39 named storms (32%) - Apply the Poisson distribution to this new number of storms 50-Year Probability Calculations - Apply the binomial distribution to the annual-average probabilities (e.g., 50- Year Prob. = 1 - (1 - One-Year Prob.) 50 - For example, if the individual-year probability is 2%, the 50-year probability would be: 50-Year Prob. = 1 - (1 – 0.02) 50 = 63%

Current Year and Climatological Probabilities ( ) CountryNS Prob. (50 Miles) H Prob. (50 Miles) MH Prob. (50 Miles) The Bahamas66% (72%)40% (45%)21% (24%) Cuba64% (70%)39% (44%)19% (22%) Haiti33% (38%)18% (21%)8% (9%) Jamaica32% (37%)15% (17%)6% (7%) Mexico72% (78%)39% (44%)13% (15%) Nicaragua24% (27%)10% (11%)5% (6%) Puerto Rico29% (33%)13% (15%)4% (5%) Climatological probabilities are in parentheses

50-Year Probabilities CountryMH Prob. (50 Miles) The Bahamas>99% Cuba>99% Haiti99% Jamaica97% Mexico>99% Nicaragua95% Puerto Rico92%

Years (Ranked by NTC)Named Storms HurricanesMajor Hurricanes Most Active 27 Years Years Years Least Active 27 Years48103 Caribbean Activity – Ranked by Observed NTC ( )

Years (Ranked by NTC)Named Storms HurricanesMajor Hurricanes Most Active 27 Years Years Years Least Active 27 Years41125 Caribbean Activity – Based on August Hindcast NTC ( )

Observed (Hindcast)Named Storms HurricanesMajor Hurricanes Most Active 27 Years99% (99%)94% (93%)76% (69%) Years % (98%)78% (80%)43% (43%) Years % (91%)62% (65%)26% (36%) Least Active 27 Years83% (78%)31% (36%)11% (17%) Caribbean Probability – Based on Poisson Distribution

Goldenberg et al. (2001)

ATLANTIC THC STRONG ATLANTIC THC WEAK POSITIVE AMO NEGATIVE AMO CAT TRACKS 79 Years 78 Years 86 Major Hurricane Days 30 Major Hurricane Days

Positive AMO Negative AMO

Positive AMO Negative AMO

TEN COLDEST ASO NINO 3.4 ( ) TEN WARMEST ASO NINO 3.4 ( ) Hurricane Days 5.5 Hurricane Days

TWENTY COLDEST ASO NINO 3.4 ( ) TWENTY WARMEST ASO NINO 3.4 ( ) Hurricane Days 28.5 Hurricane Days

Years (Ranked by ASO Nino 3.4) Named Storms HurricanesMajor Hurricanes Coolest 27 Years Years Years Warmest 27 Years49209 Caribbean Activity – Based on ASO Nino 3.4 ( )

Future Work -Investigate precursor steering current patterns for Caribbean/Central American landfall -Create shorter period user-selected probabilities for landfall using climatological storm frequency in the Caribbean/Central America

Arago’s Admonition: “Never, no matter what may be the progress of science, will honest scientific men who have regard for their reputations venture to predict the weather.”