Bryan Norcross: The hurricane Andrew anniversary and a couple of systems to watch in the Atlantic
A robust disturbance has moved off Africa. The National Hurricane Center is giving it a medium chance of developing before it gets to the vicinity of the Caribbean islands.
Tropical activity explodes in Pacific while Atlantic development odds rise
As the Pacific basin continues to roar with tropical activity fueled by El Niño, the Atlantic basin is now seeing increased odds for storm development. FOX Weather Hurricane Specialist Bryan Norcross breaks down his exclusive analysis on the growing tropical threats across both regions.
Updated at 8:49 A.M. ET on Monday, August 24.
34 years ago today
So many things happened between 2:00 a.m. and 8:00 a.m. that morning, it's hard to believe it was only 6 hours. At about 2:00 a.m., it became clear that the worst of Hurricane Andrew was going to attack South Dade. It was also clear that Andrew would be about as bad as any hurricane anywhere, anytime.
This image juxtaposes a piece of lumber driven clean through a Florida palm tree by Hurricane Andrew against an identical scene from a Category 5 storm in Puerto Rico decades earlier.
I show this picture a lot because how often does this happen? It turns out, a board pierced a palm tree at least once before. It was during the Category 5 hurricane that devastated Puerto Rico in 1928. But I've never seen another picture like it, except for the piece of plywood that split a palm tree… also in Andrew.
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Imagine the forces involved to pick up a piece of wood and propel it end on into a tree 40 feet up. Or flip cars in their garage. Or myriad other horrible and insane things that went on that morning.
This iconic radar image was captured at 4:35 AM. The front side of the eyewall had just reached Homestead Air Force Base. The assault on South Dade County – the suburban area south and southwest of Miami – was underway.
Hurricane Andrew radar (NWS Miami)
The National Hurricane Center was located in a high-rise on U.S. 1 where you see the + sign. At 4:50 AM, they measured 164 mph gusts at the top of their building, about 200 feet above the ground. The winds were likely higher than that because the anemometer lost one of its cups at some point and eventually failed. They estimated that the peak winds occurred at about 5:00 AM.
Andrew traveled just north of due west. The NHC got the very northern edge of the eyewall.
The radar succumbed to the onslaught 6 minutes after that image was taken at 4:41 AM. It blew off its pedestal crashing onto the roof of the building 13 minutes after that, just after the 164-mph gust.
It was a stunningly close call for South Beach, the Port of Miami, the international airport, and downtown Miami, which now contains a forest of buildings with some pushing 100 stories high. They are only 6 to 8 miles away from that former NHC location.
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Why did things happen during Hurricane Andrew that we don't see in other hurricanes when the top winds are "only" analyzed to have been 165 mph? My take is that the gusts were extreme. The relationship between the sustained winds and the speed of the gusts is called the gust factor. A typical gust factor of 1.4 applied to 165 mph winds yields gusts of about 230 mph. Fierce for sure. But then there is the duration of the gusty winds. The more tornado-level gusts that occur at one location, the more likely it is that catastrophic damage will occur and extreme and unusual things will happen.
Those purple smudges in the top of the eyewall in the radar image came from a strong embedded cell – a so-called mesocyclone – that rotated over South Dade. It was likely a gust machine, something like a tornado embedded in a hurricane eyewall. I think that accounted for the off-the-charts events of that Monday morning 34 years ago.
This week in the Atlantic
A robust disturbance has moved off Africa. The National Hurricane Center is giving it a medium chance of developing before it gets to the vicinity of the Caribbean islands. The atmospheric environment is marginally conducive to development, but it's still going to have to deal with leftover Saharan dust and El Niño-driven upper-level winds.
Long-range computer forecasts mostly turn it north before it reaches the islands, though that's not set in stone. We'll see how it develops this week.
Tropical disturbance in the Atlantic basin
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Many of the computer simulations that show it surviving its encounter with the dust and hostile upper winds predict it will turn into a hurricane as it heads north of the Caribbean. That wouldn't be until next week, so it's nothing to think too hard about at this point.
Farther north, the system near Bermuda is showing more immediate promise of development. The National Hurricane Center has its odds in the medium range, as well. There's a fair chance it will briefly get named Dolly, but it won't have any significant effect on land.
In the Pacific
There is a lot going on, but Tropical Depression Moke is the only direct threat to land, and it's not much. Rain will finally taper off from east to west across the state beginning later today. Spotty rainfall is still possible on the high elevations of the Big Island and Maui.
Tropical activity across the Pacific basin
To the east, Iselle and the other storms that are expected to form behind it will generate strong swells and large waves along the Pacific coast of Mexico and California.