[Willie Green]

Well I was about to ask somebody on the previous thread what an "eyewall replacement cycle" was,
but the mods locked the thread and I forget who I was going to ask.

[Peach]

NWS saying there is a slight chance that eyewall replacement will diminish the hurricane to Category 4.

[bannie]

Strategerist knows stuff: Ask him/her.

:-p

[newzjunkey]

As tropical cyclones reach this threshold of intensity, they usually - but not always - have an eyewall and radius of maximum winds that contract to a very small size, around 10 to 25 km [5 to 15 mi]. At this point, some of the outer rainbands may organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture and momentum. During this phase, the tropical cyclone is weakening (i.e. the maximum winds die off a bit and the central pressure goes up). Eventually the outer eyewall replaces the inner one completely and the storm can be the same intensity as it was previously or, in some cases, even stronger.

[Rennes Templar]

lol...a hazard of FR threads...

[nascaryankee]

From NOAA.gov

"Concentric eyewall cycles" (or "eyewall replacement cycle" ) naturally occur in intense tropical cyclones , i.e. major hurricanes (winds > 50 m/s, 100 kt, 115 mph) or Catories 3, 4, and 5 on the Saffir-Simpson scale. As tropical cyclones reach this threshold of intensity, they usually - but not always - have an eyewall and radius of maximum winds that contract to a very small size, around 10 to 25 km [5 to 15 mi]. At this point, some of the outer rainbands may organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture and momentum. During this phase, the tropical cyclone is weakening (i.e. the maximum winds die off a bit and the central pressure goes up). Eventually the outer eyewall replaces the inner one completely and the storm can be the same intensity as it was previously or, in some cases, even stronger. A concentric eyewall cycle occurred in Hurricane Andrew (1992) before landfall near Miami: a strong intensity was reached, an outer eyewall formed, this contracted in concert with a pronounced weakening of the storm, and as the outer eyewall completely replaced the original one the hurricane reintensified. Another example is Hurricane Allen (1980) which went through repeated eyewall replacement cycles -- going from Categrory 5 to Category 3 status several times. To learn more about concentric eyewall cycles, read Willoughby et al. (1982) and Willoughby (1990a).

It was the discovery of concentric eyewall cycles that was partially responsible for the end of the U.S. Governements's hurricane modification experiment Project STORMFURY, since what the scientists had hoped to produce through seeding was happening frequently as a natural part of hurricane dynamics.

[HighWheeler]

Here is the explanation from NOAA:

"Concentric eyewall cycles" (or "eyewall replacement cycle" ) naturally occur in intense tropical cyclones , i.e. major hurricanes (winds > 50 m/s, 100 kt, 115 mph) or Catories 3, 4, and 5 on the Saffir-Simpson scale. As tropical cyclones reach this threshold of intensity, they usually - but not always - have an eyewall and radius of maximum winds that contract to a very small size, around 10 to 25 km [5 to 15 mi]. At this point, some of the outer rainbands may organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture and momentum. During this phase, the tropical cyclone is weakening (i.e. the maximum winds die off a bit and the central pressure goes up). Eventually the outer eyewall replaces the inner one completely and the storm can be the same intensity as it was previously or, in some cases, even stronger. A concentric eyewall cycle occurred in Hurricane Andrew (1992) before landfall near Miami: a strong intensity was reached, an outer eyewall formed, this contracted in concert with a pronounced weakening of the storm, and as the outer eyewall completely replaced the original one the hurricane reintensified. Another example is Hurricane Allen (1980) which went through repeated eyewall replacement cycles -- going from Categrory 5 to Category 3 status several times. To learn more about concentric eyewall cycles, read Willoughby et al. (1982) and Willoughby (1990a).

It was the discovery of concentric eyewall cycles that was partially responsible for the end of the U.S. Governements's hurricane modification experiment Project STORMFURY, since what the scientists had hoped to produce through seeding was happening frequently as a natural part of hurricane dynamics.

[MikefromOhio]

An eyewall replacement cycle is when the inner eyewall erodes and an already formed outer eyewall takes it's place.


Hurricane Gilbert had something like 3 distinct eyewalls at one point.

Generally a replacement means the storm weakens a little, however, since the newer eyewall is a bit further away from the eye itself, the max winds field can expand and potentially cause more damage.

[spunkets]

"what an "eyewall replacement cycle" was"

Imagine the vortex of water going down the drain. It has a fast circular flow with an open center. If you stick your hand in the water near, but not too close to the vortex, you create sheer. You're slowing the outer flow and that will cause the flow around the vortex to become unstable. It will wobble. The new stable point it comes to is the new "wall". It's a different slope and rotational speed.

The same happens when the 'cane nears land. The land casuses the shear.