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By Steve Letro
Meteorologist in Charge
Jacksonville
National Weather Service
So...
El Niño has come back, the forecast numbers of Atlantic hurricanes is
down, and we can all relax and take a deep breath, right? After all, we’ve
been conditioned over the last couple of decades to accept that El Niño
seasons produce fewer total storms, fewer hurricanes, and fewer major hurricanes
than neutral or La Niña seasons. So... why shouldn’t we feel like
we can take at least a short break from the constant preparation and urgency
of busier seasons? In the words of a popular sportscaster; not so fast, my friend!
While it is basically true that strong El Niño seasons
produce fewer storms overall, this says nothing about the behavior of any individual
storm within that season, and certainly does not rule out the possibility of
a devastating major hurricane crossing the U.S. coast. In fact, if we look back
at some of the more infamous hurricanes in Florida history... storms such as
Andrew, Betsy, Donna, or the 1935 hurricane, we find that they all occurred
in seasons that would be otherwise considered “quiet” from the standpoint
of pure numbers!
Or, consider that the “active” 2000-2001 seasons
produced 14 and 15 named storms, respectively, with a total of 17 hurricanes,
yet not a single hurricane made landfall in the United States. The 2002 season,
though, which was affected by El Niño, with lower numbers of forecast
storms, produced Hurricane Lili which did make landfall, and actually came within
a few hours of crossing the Louisiana coast as a devastating Category 4 storm.
In addition, Florida had close calls with several named storms during the 2002
season, any of which could have been a much more serious problem had atmospheric
conditions been just a little different.
The key thing is to realize that El Niño’s
major influence is to produce increased wind shear over the deep tropical Atlantic,
the so-called “Main Development Region” between the Lesser Antilles
and the African coast, which inhibits development in that area. This is the
area where the infamous Cape Verde type hurricanes form, so this is a good region
to keep under control. However, El Niño seems to have somewhat less influence
on storms forming farther to the west and north of that region... including
the western Caribbean Sea and the Gulf of Mexico... home to some of the warmest
water (i.e., hurricane fuel) in the western hemisphere.
This area is, in fact, where we saw the majority
of the 2002 storms form, and is significant because it means that many develop
within just a few hundred miles of Florida instead of thousands of miles away
nearer to Africa. Such storms are often virtually in our backyard when they
form, and raise the specter of the ultimate meteorological nightmare... a storm
rapidly increasing in intensity as it approaches the coast, with little time
to react or adequately evacuate. This very nearly happened with Opal in the
Florida panhandle in 1995, and again in 2002 with Lili along the Louisiana coast.
It was most fortunate that both of these storms weakened just as rapidly before
they made landfall, but it would be foolish to think that we will always be
that lucky.
For
that matter, even in the most pronounced El Niño-dominated seasons, there
often seems to be at least one storm that finds a window of opportunity to overcome
the overall hostile environment and develops into a troublemaker. The 1992 season,
by any numbers standpoint, would be considered “quiet” if not for
one storm which took advantage of just such an opportunity. That, of course,
was Andrew, one of just 3 hurricanes to ever strike the United States at Category
5 strength on the Saffir Simpson scale. Texans learned the same lesson in 1983
when Alicia... a major hurricane... devastated the Houston area in an El Niño
season which otherwise produced a total of only 4 named storms.
The emergency management community has long understood
that the mere presence of El Niño conditions is no guarantee whatsoever
of a safe hurricane season... even though the total number of storms may be
lower. As individuals, we need to base our preparedness actions each year on
the assumption that this might be the year we get the “big one”...
El Niño or not!
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