Cat 5 Hurricane Irma awful, but not the strongest in history

HOUSTON - Irma is a monster. It's a killer. It's not coming to Texas. It may be going to Florida. If not there, than the Carolinas or Georgia.

But, be weary of claims that Irma is the 'worst' hurricane in the Atlantic in history. (The 'Atlantic' is defined as the basin extending from the open ocean, including the Gulf of Mexico and Caribbean Sea.) No doubt, it's among the worst and will rank in the top 10 hurricanes in recorded history, but reliable hurricane history only goes back loosely to the 1890s. The satellite era of recording every hurricane only goes back to the early 1960s. Planes weren't used to measure minimum central pressure until about 1945. Some hurricanes slipped through the cracks of being observed prior to 1960 and others were not properly sampled before WWII. Our recorded hurricane history is thus extremely limited so this can not be placed in league with the countless hurricanes in the tens of millions of years before we got here. To claim any superlative in science as being, "the worst" is inherently inaccurate... But in the spirit of our very brief human time-scale history and the human need to seek validation, we can say Irma is a big one.

Hurricane Allen in 1980 packed strongest winds in Atlantic basin with max sustained of 190mph. (Compared to Irma's 185mph.)

However, a better way to measure storm intensity is looking at air pressure of a hurricane -- specially its minimum central pressure. Hurricane Wilma packed the lowest pressure in Atlantic basin with 882mb (compared to Irma's 914mb at its peak.) 
 
Why do we look to its minimum central pressure instead of peak wind speed in judging a hurricane's strength? Because, it's impossible to sample what the winds are doing at all times inside a storm, as we simply don't have a large network of instruments in the ocean measuring them. With the exception of a few buoys here and there, we rely on airplane recon to take measurements. If the system peaks while there's no airplane inside the hurricane in the strongest quadrant, that wind speed could go unobserved. However, air pressure in the core is more easily measured, but faces the similar observation limitations. (Satellites can only estimate barometric pressure.)
 
Pressure also indicates depth of a cyclone. The deeper (lower the pressure) the stronger. 


Here are some Irma superlatives, directly from Dr. Philip Klotzbach, Colorado State University: 
  • Irma is the strongest hurricane on record to hit the Leeward Islands, as defined as 15°-19°N, 65°-60°W. (However, it's not the strongest hurricane on record, in the Atlantic.)
  • Irma's had the longest stint of 180+mph winds in recorded history, at 24+ hours straight. This beats 1980's Hurricane Allen time as a 180mph+ hurricane. (Allen peaked at 190mph, briefly.) 
  • "Irma has now generated more Accumulated Cyclone Energy (ACE) than all 14 storms combined in the 2013 Atlantic hurricane season." -@PhilKlotzbach - (Twitter)
  • "#Irma has now had winds of 185 mph for 33 hrs - no other TC around the globe has been this strong for so long in satellite era (since 1966)." -@PhilKlotzbach - (Twitter)

Here are some Irma superlatives, from Eric Blake, National Hurricane Center (@EricBlake12 on Twitter): 

  • "Irma has now maintained 185 mph winds for 24 hours - no Atlantic or eastern Pacific #hurricane has ever stayed this strong for so long."

It should be noted: When I first wrote this article, the minimum central pressure for Irma was listed at 916mb. That was weaker than the open-Atlantic's Hurricane Isabel in 2003, which had 915mb. Since publishing, it's been updated that Irma had a minimum central pressure of 914mb. We're splitting hairs here over 1mb between Isabel and Irma -- and it's arguably not statistically significant, but that would technically place Irma as the top hurricane in the Atlantic east of Florida and the Lesser Antilles. Keep in mind with these stats: I say it's not statistically significant because there may not have been an airplane in Isabel's eye at it's absolute peak back in 2003, so it's possible it was even lower than 915mb. Perhaps I should say it's not, observationally significant. These are only recorded minimum central pressures. To declare Irma is, 'the strongest ever, in the Atlantic' is still not accurate, all things considered.

That's how I see it, from my perch at the auxiliary KHOU studios, here at Houston Public Media, KUHT-TV.
 
-Brooks
 

© 2017 KHOU-TV


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