Since we are now in hurricane season, I wanted to say a few things about these tropical tempests. First of all, they do not start out as hurricanes. The stages of development are: tropical wave (just a cluster of thunderstorms), tropical depression, tropical storm (this is when they get a name), and, finally, hurricane. Hurricanes are then rated on a scale called the Saffir-Simpson Scale. Category 1 is at the low end of the scale, with winds of at least 74 mph, while category 5 is at the high end of the scale, with winds stronger than 156 mph.
I have found that the public perception tends to be that a hurricane’s story is sort of finished once the big damage occurs on the coast, but I’ll tell you what: nothing could be further from the truth. Of the three main threats posed by hurricanes, freshwater flooding, sometimes very far away from initial landfall, is one of them.
Perhaps the most horrific example of this occurred in August of 1969, in Nelson County, Virginia, near Charlottesville, when the remnants of powerful hurricane Camille, which had ravaged the Mississippi Coast with 190 mph winds and a storm surge of 24 feet, turned north and then east over the central Appalachians, where weather conditions then came together to unleash a deluge of biblical proportions, with 27 inches of rain falling in only 8 hours. One hundred fifty-six people in Nelson County lost their lives in the calamitous flash flooding that ensued (and Nelson County was only sparsely populated).
To get a sense of this kind of rainfall rate, just imagine the heaviest rain you’ve ever seen, and then imagine it going on for eight straight hours. Again, remember the title of this column. You’ve got to keep watching the storm after the big damage has been done where they made landfall. (Hurricanes derive their energy from warm ocean water and, wind-speed-wise, they weaken rather rapidly once inland.)
So “Keep Watching It” means you’ve got to follow the storm during its entire trek across the Eastern USA and Maritime Canada, irrespective of where it makes initial landfall, because a heavy rain threat will exist all along its track.
Let me give you another example of the inland flood threat that hurricanes pose. It occurred only six years ago, in 2011, and it happened right here in New England, when Hurricane Irene caused devastating flooding in Vermont. More than 2,400 roads and 300 bridges (including historic covered bridges) were destroyed or damaged (NOAA).
And to make the point yet again, Vermont is an INLAND location. So these storms of tropical origin must always be followed after landfall, since the airmass itself remains of tropical origin, capable of producing extreme rainfall, even though the hurricane’s winds have wound down significantly.
A final, personal example: back in 1999 when I lived in Bangor, I received exactly 1 FOOT of rain in two separate events, six days apart. The remnants of Hurricane Dennis delivered 6 1/2 inches and then the remnants of Floyd came along to make it an even foot. To put that in perspective, that is almost one-third of Bangor’s average annual precipitation, in less than one week.
Say, if you wish to track hurricanes this season, the best site to go to is the National Hurricane Center’s homepage. Just google “NHC”, and you will get there quickly.
I’ll close by saying that I hope everyone is having a good start to summer.
Remember your lightning safety rules when out and about. When you hear thunder, seek shelter at once.
For the hearing impaired, it’s “When you see the flash, you have to dash (to safety)”
Always remain sheltered for 30 minutes after the last thunder is heard or the last lightning flash is seen.
Ted Shapiro holds the Broadcast Seal of Approval from both the American Meteorological Society and the National Weather Association. An Alexandria, Va. native, he has been chief meteorologist at WAGM-TV since 2006. Email him at tshapiro@wagmtv.com.
