Midget to Monster Hurricane

[Ptarmigan]

I know Hurricane Katrina started as a really small hurricane with hurricane force winds extending up to 15 miles from the center when it hit South Florida. Than once it went over the Gulf of Mexico, it exploded into a monster, one of the largest hurricane on record. Same went with Ivan. I wonder if there have been other hurricanes that started as small and grew into monsters or vice versa, large than small?

[wxman57]

Here's the answer I posted at the KHOU forum to your question:

I've been studying hurricane wind field size very closely over my nearly 3 decades forecasting hurricanes. In particular, I've performed intense studies of wind field size since 2005.

What I've observed is that just about all hurricanes grow in size as they become better-organized, but not necessarily as they intensify. For example, Wilma was the most intense hurricane on record in the Atlantic basin but it was also just about the smallest while it was in the Caribbean. Neither Katrina nor Ivan was anywhere close to a "midget" hurricane at any time. Same would go for Rita. All three hurricanes grew in size along a typical curve for the most part. Katrina's wind field wasn't large when it hit Florida because it was just organizing.

Hurricane wind radii (39, 58, 74 mph wind fields) typically do increase as a TC organizes, as I said. But there are reasons that a hurricane can increase significantly in size over a short period of time. From what I've observed, rapid growth in wind field size can occur when an already intense hurricane encounters an environment that results in a sudden reduction of surface winds. Again, think of Wilma. It was one of the smaller hurricanes observed in the Atlantic Basin while it was in the Caribbean near peak intensity. But when Wilma interacted with land over the NE Yucatan (and again across Florida) it grew to one of the largest hurricanes ever observed in the Atlantic basin.

Think about what happened. Wilma's circulation had a great deal of kinetic energy (energy of wind in motion). As the surface circulation was disrupted by low-level turbulence (land interaction), that kinetic energy was mostly conserved by an expansion of the wind field. We've sound many cases of significant wind field expansion due to land interaction. Katrina moved across Florida, remember? But Katrina's wind field expansion was aided greatly by an eyewall replacement cycle prior to landfall. Peak winds near the center dropped off and a larger outer ring of intense winds developed. This greatly increased Katrina's area of hurricane force winds prior to landfall. So even though Katrina was just a Cat 3 at landfall, it produced a very large storm surge and widespread damage. It was the size of Katrina's wind field that was mostly responsible for the large surge. Same with Rita as far as the surge.

A local weather company has developed a new hurricane scale as an improvement over Saffir-Simpson. You can see a graphic of Katrina's size and intensity growth at the beginning of the document (farthest right of the 3 images). Note how Katrina grew steadily in size from when it developed, though there were spurts of growth all along the way.

http://katrina.impactweather.com/hsi/hsi.pdf

Oh, and as for the other way around - monster to midget. I can't recall any instance of a large intense hurricane becoming a small intense hurricane.

[Ptarmigan]

Here's the answer I posted at the KHOU forum to your question:

I've been studying hurricane wind field size very closely over my nearly 3 decades forecasting hurricanes. In particular, I've performed intense studies of wind field size since 2005.

What I've observed is that just about all hurricanes grow in size as they become better-organized, but not necessarily as they intensify. For example, Wilma was the most intense hurricane on record in the Atlantic basin but it was also just about the smallest while it was in the Caribbean. Neither Katrina nor Ivan was anywhere close to a "midget" hurricane at any time. Same would go for Rita. All three hurricanes grew in size along a typical curve for the most part. Katrina's wind field wasn't large when it hit Florida because it was just organizing.

Hurricane wind radii (39, 58, 74 mph wind fields) typically do increase as a TC organizes, as I said. But there are reasons that a hurricane can increase significantly in size over a short period of time. From what I've observed, rapid growth in wind field size can occur when an already intense hurricane encounters an environment that results in a sudden reduction of surface winds. Again, think of Wilma. It was one of the smaller hurricanes observed in the Atlantic Basin while it was in the Caribbean near peak intensity. But when Wilma interacted with land over the NE Yucatan (and again across Florida) it grew to one of the largest hurricanes ever observed in the Atlantic basin.

Think about what happened. Wilma's circulation had a great deal of kinetic energy (energy of wind in motion). As the surface circulation was disrupted by low-level turbulence (land interaction), that kinetic energy was mostly conserved by an expansion of the wind field. We've sound many cases of significant wind field expansion due to land interaction. Katrina moved across Florida, remember? But Katrina's wind field expansion was aided greatly by an eyewall replacement cycle prior to landfall. Peak winds near the center dropped off and a larger outer ring of intense winds developed. This greatly increased Katrina's area of hurricane force winds prior to landfall. So even though Katrina was just a Cat 3 at landfall, it produced a very large storm surge and widespread damage. It was the size of Katrina's wind field that was mostly responsible for the large surge. Same with Rita as far as the surge.

A local weather company has developed a new hurricane scale as an improvement over Saffir-Simpson. You can see a graphic of Katrina's size and intensity growth at the beginning of the document (farthest right of the 3 images). Note how Katrina grew steadily in size from when it developed, though there were spurts of growth all along the way.

http://katrina.impactweather.com/hsi/hsi.pdf

Oh, and as for the other way around - monster to midget. I can't recall any instance of a large intense hurricane becoming a small intense hurricane.

Good post! I also post at KHOU too.

[MGC]

The rating have both Camille and Katrina at about a 36 at landfall, yet Katrina's damage swath was far more extensive than Camille. I thought the objective of the new rating system was to normalize the damage potential for individual hurricanes. Am I misreading the graph?...MGC

[wxman57]

The rating have both Camille and Katrina at about a 36 at landfall, yet Katrina's damage swath was far more extensive than Camille. I thought the objective of the new rating system was to normalize the damage potential for individual hurricanes. Am I misreading the graph?...MGC

The HSI was not developed specifically to normalize damage potential for individual hurricanes. It's just a new way to estimate the potential destructive power of an approaching hurricane. The variables relating to actual damage go far beyond just size and intensity.

At landfall, both Camille and Katrina would have scored 36 points on the HSI. However, Katrina scored 23 of 25 size points and Camille only 14 size points out of a possible 25. So Katrina was considerably larger than Camille though much less intense. Katrina's larger wind field led to a slightly larger storm surge. But the angle that Katrina hit the coast was different by about 30 degrees from Camille's angle of approach. This is significant in that Katrina's more southerly approach resulted in a greater easterly wind fetch along the LA/MS coasts prior to its arrival. This resulted in a greater "set-up tide" across southeast Louisiana and Mississippi. With Camille, NE-ENE winds prior to its arrival actually resulted in tides 3-5 feet below normal on evening Camille approached the coast. This was not the case with Katrina, as the easterly winds resulted in tides above normal prior to the arrival of the storm surge.

One of the main differences (damage-wise) between the two was that the levees in New Orleans held during Camille and failed after Katrina passed. Had it not been for the failure of the levees in New Orleans, there may have been much less damage across southeast Louisiana and the damage would have been mostly confined to the Mississippi coast as it was with Camille.

Camille certainly produced considerably more wind damage across Mississippi than did Katrina, and that wind damage extended much farther inland. So, overall, the amount of damage wasn't that much different if you remove the costs of the levee failures in New Orleans.

[jasons2k]

Seems logical to me. Interesting that Carla tops the chart @ landfall.

[MiamiensisWx]

I believe Camille actually resulted in levee failures across extreme SE Louisiana in the vicinity of the Mississippi Delta and the Buras region. The storm surge caused considerable flooding in those regions, though the greater New Orleans metropolitan area was largely unscathed from surge flooding and damages, though eastern New Orleans (closest to the center) did receive some locally extensive wind damages. Here is the official TCR for Camille.

http://www.nhc.noaa.gov/archive/storm_wallets/atlantic/atl1969-prelim/camille/TCR-1969Camille.pdf

Excerpt:

"The major river flooding in the Gulf Coast area came as Camille's center moved east of lower Placquemines Parish in southeastern Louisiana. Northerly winds pushed a massive surge through the marshes, over both east and west bank Mississippi River levees in the region from Empire southward, removing almost all traces of civilization. Every building from Port Sulphur southward sustained extensive wind and water damage and only six structures remained at Buras where 6,000 persons had made their home. At Boothville the water was 17 feet deep with 54 inches inside the Weather Bureau Office."

[DanKellFla]

Wow, that HSI is great. I have been trying to explain to people why one Cat 2 is different than another Cat 2. Everybodys eyes glaze over when I start talking about windfield size.