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Katrina at peak intensity
Left by Katrina
Houston fleeing category 5 Rita
Top photo coutesy of Weather Underground. Rest of the photos courtesy of Wikipedia
Since covering hurricanes there have been eight hurricanes that have reached the rarifed category 5 threshold. Few storms anywhere on earth manage to top the magic maximum sustained winds of 156 mph or greater, that’s why only eight out of hundreds have achieved this over the past 6 years. Only thing is, eight in 6 years is exceptionally more than normal, but a mature warm multidecadal oscillation may explain the rise in cat 5 storms.
Rare for many reasons and that’s a very good thing. Not only have I witnessed and covered the eight cat 5 Atlantic storms sice 2003 but, two storms made landfall at those intensities, both in the same season and both within the Caribbean Sea. That tells one story. The remarkable and unprecidented four cat 5’s of 2005 (the mega year), 2 reached cat 5 in the Gulf, roughly in the same region and 2 cat 5’s formed in another similar region in the Caribbean. Why? because of the ocean temperature profile. It takes a perfect atmospherics environment combined with exceptionally deep, warm to near hot water in a broad area to supply high octant fuel to drive these massive machines. There are three key regions that can allow a hurricane to achieve this intensity. The Caribbean is the no. 1 hot house for the deepest, warmest waters in all of the Atlantic basin, No. 2 is the Gulf of Mexico, both support 85-90 degree waters in areas 200-500 feet below the surface, where a hurricane’s winds cannot churn cooler waters under the warm, even hot skin of the ocean. The Caribbean Sea’s western side, near the Yucatan is thee warmest, deepest area and supported Hurricane Wilma, which acheieved the lowest pressure in any Atlantic hurricane on record of 882mb. The loop current supplies the already warm Gulf of Mexico with increased depth of warmth. Skin temperatures can get as hot as 92 degrees and 90 degrees for a few hundred feet below the surface thanks to the loop current and it’s associated eddies that spin off the main current that run up from the Caribbean Sea, loops around the Gulf and then heads out through the Florida Straits and up off the East Coast of the United States as the Gulf Stream. The Gulf Of Mexico, sure is warm and deep, but in order for the cat 5’s the blow up, these systems must cross the loop current in order to acheive maximum power. Both Katrina and Rita intensified at some of the most rapid rates due to it’s crossing of the loop current. Another major factor is that, atmospherically there must be low to lower than normal air pressure, moist air and literally an absense completely of wind shear in the mid to upper levels of the atmosphere. It is possible to get cat 5 storms in both cool AMO’s and El Nino years, both of which tend to restrict both amount of storms developing and power achievable. El Ninos tend to enhance upper shear across the Caribbean and Atlantic and cool AMO’s keep overall ocean temperatures cooler. However even El Nino years have seen periods in which storms have blossomed to cat 5’s (exp Andrew in 92), not everywhere experiences wind shear AND IN COOL AMO’s the Caribbean and Gulf can still have very warm, deep water, but warm AMO’s tend to bring waters 1-3 degrees ABOVE normal, therefore maximizing or increasing the theoretical “maximum potential intensity” values, that was clearly seen I believe in 2005 when ocean surface temperature and corresponding depths where 1-3 above normal in the Gulf, coupling this with the loop current and getting two well developed systems right over the loop current, bang, you get two explosively intensifying storms. (Katrina and Rita).
Rare for many reasons and that’s a very good thing. Not only have I witnessed and covered the eight cat 5 Atlantic storms sice 2003 but, two storms made landfall at those intensities, both in the same season and both within the Caribbean Sea. That tells one story. The remarkable and unprecidented four cat 5’s of 2005 (the mega year), 2 reached cat 5 in the Gulf, roughly in the same region and 2 cat 5’s formed in another similar region in the Caribbean. Why? because of the ocean temperature profile. It takes a perfect atmospherics environment combined with exceptionally deep, warm to near hot water in a broad area to supply high octant fuel to drive these massive machines. There are three key regions that can allow a hurricane to achieve this intensity. The Caribbean is the no. 1 hot house for the deepest, warmest waters in all of the Atlantic basin, No. 2 is the Gulf of Mexico, both support 85-90 degree waters in areas 200-500 feet below the surface, where a hurricane’s winds cannot churn cooler waters under the warm, even hot skin of the ocean. The Caribbean Sea’s western side, near the Yucatan is thee warmest, deepest area and supported Hurricane Wilma, which acheieved the lowest pressure in any Atlantic hurricane on record of 882mb. The loop current supplies the already warm Gulf of Mexico with increased depth of warmth. Skin temperatures can get as hot as 92 degrees and 90 degrees for a few hundred feet below the surface thanks to the loop current and it’s associated eddies that spin off the main current that run up from the Caribbean Sea, loops around the Gulf and then heads out through the Florida Straits and up off the East Coast of the United States as the Gulf Stream. The Gulf Of Mexico, sure is warm and deep, but in order for the cat 5’s the blow up, these systems must cross the loop current in order to acheive maximum power. Both Katrina and Rita intensified at some of the most rapid rates due to it’s crossing of the loop current. Another major factor is that, atmospherically there must be low to lower than normal air pressure, moist air and literally an absense completely of wind shear in the mid to upper levels of the atmosphere. It is possible to get cat 5 storms in both cool AMO’s and El Nino years, both of which tend to restrict both amount of storms developing and power achievable. El Ninos tend to enhance upper shear across the Caribbean and Atlantic and cool AMO’s keep overall ocean temperatures cooler. However even El Nino years have seen periods in which storms have blossomed to cat 5’s (exp Andrew in 92), not everywhere experiences wind shear AND IN COOL AMO’s the Caribbean and Gulf can still have very warm, deep water, but warm AMO’s tend to bring waters 1-3 degrees ABOVE normal, therefore maximizing or increasing the theoretical “maximum potential intensity” values, that was clearly seen I believe in 2005 when ocean surface temperature and corresponding depths where 1-3 above normal in the Gulf, coupling this with the loop current and getting two well developed systems right over the loop current, bang, you get two explosively intensifying storms. (Katrina and Rita).
Hurricanes of category 5 intensity really facinate me for many reasons.
1) They produce the most breathtaking and beautiful structures from space.
2) They generate a mindboggling amount of energy and heat.
3) The sustained wind speeds achieved are breaktaking, yet so destructive. Thankfully few storms that reach this rare criteria actually make landfall at such intensity. The few that do, create such raw power and destruction to life and property.
Few hurricanes reach their maximum potential like stated already. There is a limitation in just how strong or powerful these systems get, why they stop at a certain threshold is unkown, but why certain storms only get to cat 3 rather than cat 5 is likely due to a limited depth of the “mixed layer” where waters are warm enough to support tropical cyclones, we must keep in mind that even storms that travel over waters of 80-85 degrees down to a depth of 200 feet below the surface, still churn colder waters that reside BELOW the 200 foot level, therefore limiting the amount of intensification achieveable. Thise mighty cat 5’s must have 1) 1-4F ABOVE NORMAL SST’s and depths probably in the order of 500 feet or lower to restrict the amount of cold water upwelling to will automatically put a limit on intensity of that storm.
That’s why there is a select few areas that can support these rare storms. Even when storms roam these cauldrons of , deep, hot waters like in the western Caribbean, shear will likely restrict things or when shear is absent and a storm gets into the what looks like 88 degree waters, may 1) only have a depth of 150 feet of that high surface heat or the system may cross a cold eddy… To get perfect atmospheric conditions and adequate ocean profiles, is extremely difficult.
However when they do, they produce some of the most intense power any storm on the face of earth can produce…. Note the gusts!
WILMA 2005 (882mb):
WESTERN CARIBBEAN SEA.. MAX SUS WINDS 185 MPH, GUSTS 200 + MPH.
KATRINA 2005 (902mb):
CENTRAL GULF OF MEXICO.. MAX SUS WINDS 175 MPH, GUSTS 215 MPH.
Apparently, When Katrina peaked over the loop current to a 175 mph, Katrina kicked up 50 foot waves in the Gulf and with the expansion of it’s windfield to over 200 miles out from the center, the enormity of such energy is unthinkable. To fuel such a system, is hard to comprehend as the inflow at the surface must have been to a maximum, a lack of incoming fuel through hot deep waters needed to be in constant supply to keep this thing going even for 1 hour, never mind 12 + hours at “peak intensity” The inner structure would have likewise been perfect, with the updraft and downdraft columns working perfectly as well as entropy. Air at the surface and inside the top of the eye at 55,000 to 65,000 feet was likely at 30 degrees C or 88 degrees F + whilst the central dense overcoast and eyewall tops were at -120F..
RITA 2005 (895mb):
CENTRAL GULF OF MEXICO.. MAX SUS WINDS 180 MPH, GUSTS 235 MPH
IVAN 2004 (910mb):
WESTERN CARIBBEAN.. MAX SUS WINDS 165 MPH, GUSTS EST AT 200 MPH
Ivan’s eyewall not only crossed Cuba’s westernmost tip bringing wind gusts to 195 MPH but broke several records. During his weakening and then restrengthening in the east-central Gulf of Mexico he generated wave heights apparently of over 100 feet with one such wave measured at a terrifying 131 feet! Hard to comprehend. He also made landfall on the Alabama,-Florida line at category 3 intensity with winds of 130 MPH and produced at the time a record storm surge of 14 feet that destroyed five-story condo’s on Orange Beach, AL.. Winds of 90 MPH were reported 100 miles inland.
ISABEL 2003 (915mb):
WESTERN ATLANTIC.. MAX SUS WINDS 160 MPH, GUSTS 233 MPH
LANDFALLING CAT 5’S
The 2007 season was a remarkable one, not sor US landfalls but the two systems that spun off Africa that eventually became Dean and Felix rewrote the records for the only two cat 5’s to make lanfall in the same season. Never mind the fact they were both Caribbean monsters and hit within the Caribbean Sea.
DEAN 2007 (905mb):
WESTERN CARIBBEAN.. MAX SUS WINDS 175 MPH, GUSTS 200 MPH
Dean was still intensifying as the eyewall came ashore near Majahaul on the Yucatan Pennisula of Mexico. Waters were so warm and so deep as well as a literal absense of shear, the land’s frictional drag was not enough to stop the intensification process and unfortunately more or less anywhere that was within Dean’s eyewall was wiped off the face of the earth with sustained 175 mph winds and gusts to a stunning 200 mph.
FELIX 2007 (929mb):
WESTERN CARIBBEAN.. MAX SUS WINDS 175 MPH, GUSTS 200 MPH
Another intensifying system up till landfall in Belize, Central America as a 175 mph cat 5, again wind gusts were said to have topped 200 mph, again wiping everything off the map where the eyewall came ashore. With the poorer region, most homes were wooden and poorly built.
The hurricane hunters needed to abort their mission whilst flying through Felix as it was rapidly intensifying. Violent updrafts and downdrafts as well as hail, and lightning were causing extreme turbulence. Likely inhanced be the shear speed in which the storm was growing and strengthening over the western Caribbean. Both Dean and Felix followed a similar path from the deep tropical Atlantic into the southern Caribbean Sea, warmer than normal conditions within the Caribbean basin, meant higher than normal fuel to feed off.
In a later post I shall talk more about cat 5 storms and more on “rapid intensification” of Wilma, Rita and Katrina as well as Felix which I believe beat Wilma is the rapid intensification process.
Thanks for reading.
-Mark
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