Scott McDowell, Ph.D.
Sea Science Articles written for The Triton magazine
Lightning – Probability of Strikes for Boaters
Because of severe injuries and death caused by convective
(rising warm-air) storms, the National Weather Service has
compiled accurate statistics on the incidence of reported
lightning casualties in the U.S. Interesting conclusions
from this database are given below:
• Summer months have the highest number of
lightning related deaths with July being the
maximum, likely a result of outdoor recreation.
• Males experience 84% of the lightning fatalities;
over 4 times that of females.
• 91% of the death events result in a single fatality.
• Over the past 35 years there has been a 30%
decrease in lightning casualties because of
improved storm forecasting and public warnings.
Florida has experienced twice as many lightning-based casualties than any other state in the
U.S., with 468 fatalities reported in 53 years (8.8 per year). High air temperatures and frequency
of convective storms drive these statistics, as do the popularity of outdoor recreational activity
in the country’s southernmost state. In New England and along the West Coast, the probability
of lightning fatalities is low and very seasonal, whereas in Hawaii and Alaska, it is improbable.
These reportings have been supplemented in recent years by data from new satellite-based
meteorological sensors. Each year in the U.S. there are roughly 25 million lightning strikes
and 100 million strikes per second worldwide. The majority of strikes occur over land
where air rises from solar heating. Strikes are rare over the open ocean but more common
in coastal areas where warm waters can induce atmospheric convection, like over land.
A few anecdotes: Being killed by lightning is more likely in low-latitude coastal States than winning
a major lottery. Furthermore, if you are a male living in Florida and conducting an outdoor
recreational activity around 4 p.m. on a Sunday in July, your chances of being struck by lightning are
optimized. The good news is that you’ll most likely be the only person to die from that lighting strike.
With regard to lighting statistics for boaters, Boat US has compiled statistics on lightning strikes of
vessels (not persons) from insurance claims submitted to their organization by their members. While
their database does not include all vessel strikes for the entire nation, their 2010 analysis does provide
interesting results for the period 2000 through 2005:
• Nationally, the odds of a vessel being struck by lightning are about 1.2 in 1,000. In Florida however,
the strike rate is three times higher and 33% of all Boat US lightning claims were in Florida.
Scott McDowell, Ph.D.
Sea Science Articles written for The Triton magazine
• Chesapeake Bay has the second highest incidence of vessel strikes due to convection over the warm,
shallow waters of the Bay in summer.
• The majority of strikes occur on sailboats (4 per 1,000) on account of their tall masts.
• Power boats are struck less (0.5 per 1,000) but trawlers have the highest number of strikes of all
powerboats (2 per 1,000), likely because they have higher antennae and superstructures than smaller
vessels, which exist in greatest number in the database.
• Wide, multihull sailboats are struck twice as often as mono-hull sailboats, probably because they
are berthed alone rather than beside other vessels which can provide ‘shielding’ (e.g., act as adjacent
targets for lightning).
• Vessels with lower structure and antennae than their neighbors can still be hit directly by lightning so
shielding is not a guaranteed deterrent.
Lightning damage to a vessel is often readily apparent from physical damage and/or inoperable electronics.
However, there are cases when lightning-damaged wiring or electrical components did not present themselves
for many years, then finally failed or shorted out when least expected, or desired. Recommendations
for lightning preparedness for boaters are provided in my Marinas Guidebook; see reference below.
In my next Triton article, I provide information on additional lightning topics:
• How lightning is formed and how strike locations are determined.
• How far strikes can occur from a storm center.
• How to sense an imminent, local strike.
• Are you safer in seawater than freshwater lakes and pools?
• Should you jump overboard if lightning is likely to strike?
• Will a swimmer be electrocuted but not fish?
www.scottemcdowell.com
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