a question for the board

[weatherwindow]

given the long list of major storms that dramatically weakened on approach to the northern GOM coast, can anyone suggest a synoptic setup along the coast which would allow for the opposite result...a strengthening or steady state major at landfall...given the generally low dew points of the continental airmass and the high probability of higher shear, i am having difficulty specifying a realistic scenario......all input is welcome.....rich

[Jim Cantore]

an Andrew like setup

[weatherwindow]

i am thinking about the north GOM coast specifically...the lower fla peninsula is, i believe, a different case..high dew points predominate, normally well south of the westerly etc....but thanks for the response....rich

[Jim Cantore]

Of course not tracking hurricanes in 1992 I have no Idea what that setup was

maybe the setup when Camille came in

[ericinmia]

Of course not tracking hurricanes in 1992 I have no Idea what that setup was

maybe the setup when Camille came in

She was weakening also as she came in, i saw a recent analysis showing she could have weakend up to 2 cats just before landfall.

As Many mets have said, the area is not very conducive to a cat5 landfall, between dry air intrusion, land friction, fronts, etc.
-Eric

[Jim Cantore]

hmm

doesnt explain the 224mph wind gust in Biloxi

however I find that to be highly likely of an intrument error

is there anyway they can prove she wasnt a 5?

[vbhoutex]

About the only way I see a Hurricane approaching the N GOM coast and strengthening, at least in the upper categories is a Charlie like or Wilma like set up except obviously happening along the N GOM coast. This would require the storm to be heading NNE to NE in front of an approaching trough/front. That is about the only scenario I can see with this happening. After watching almost every major hurricane to hit the N GOM over several decades do this it is almost impossible not to come to a conclusion such as this imo. Obviously I have no "scientific " basis for my reasoning, just a lot of experience.

[Jim Cantore]

Opal, Ivan, Dennis, Katrina, Rita

the only way I could see it is a fairly quick moving cat 5 (15-20mph) which I dont see one going like that

The northern gulf somehow free of dry air

this would avoid the dry air weakening and give the land friction less time to weaken it

[Jim Cantore]

The thing all those hurricanes had in common was that their major impact was surge which is obviously the trend with large gulf hurricanes.

Katrinas wind damage was likely only 5-10 billion of her damage if even that much

[Derek Ortt]

yeah

approach the coast as a 1 or a 2 like Erin in 1995 did

As the NHC documented, its only those approaching the northern GOM as major hurricanes that weaken, which has me thinking that its a heat content issue

[vbhoutex]

yeah

approach the coast as a 1 or a 2 like Erin in 1995 did

As the NHC documented, its only those approaching the northern GOM as major hurricanes that weaken, which has me thinking that its a heat content issue

I presume that would be due mostly to how shallow the shelf is and how far out i goees in a lot of places along the NGOM coast.

[Jim Cantore]

another good point

half the gulf is relatively shallow

[Derek Ortt]

yeah,

the shallowness of the water and the fact that the warm water depth is even shallower in the north GOM

[Jim Cantore]

Much easier to upwell cooler water which also plays a role in this

[Jim Cantore]

"The Curse/Blessing of the northern Gulf"

[wxman57]

I don't believe that upwelling of just slightly cooler water (not cool water below 27C) could lead to such rapid weakening in just a matter of hours. I've watched many hurricanes in the past travel over some quite cool water and retain their intensity for quite a while if not even intensify.

We know that dry air intrusion in the lower levels can lead to eyewall collapse and rapid weakening in just a few hours. Ivan, Rita, Dennis, and Lili are good examples of weakening due to low-level dry air entrainment.

But the question is, what parameters must be in place to allow for intensification at landfall in the northern GoM? I think we have to look at the delicate vertical structure of the hurricane to get the answer. Hurricanes are extremely vulnerable to vertical wind shear. Wind shear can tear a hurricane apart in a matter of hours. It just so happens that as a hurricane recurves it is generally encountering increasing wind shear.

But a lack of wind shear, or, more precisely, perfect ventillation could lead to rapid intensification. I think that two examples would be Lili in 2002 and Charley in 2004. Both were northward-moving hurricanes that suddenly encountered that "perfect ventillation" associated with a weak upper-level trof to the northwest. The trof in both cases wasn't strong enough to induce shear, just better ventillation. In Charley's case, its rapid forward speed to the NNE countered what would normaly have been deadly shear, allowing Charley to intensify.

Basically, it's very difficult to achieve perfect conditions for intensification with a recurving (northward-moving) hurricane. Sometimes a very weak upper-low or trof northwest of the hurricane can enhance outflow and lead to rapid development prior to landfall. A faster-moving hurricane may have a better shot at reaching the coast before dry air intrusion causes weakening and before there's a chance for much cool upwelling.

Finally, think of all the big Cat 5s of the past - all were moving to the W-WNW south of the Bermuda high. Ventillation is generally good south of the high, and wind shear is low. That would mean that the Texas coast may be at a higher risk of being hit by an intensifying major hurricane than the northern Gulf Coast.

[DESTRUCTION5]

yeah

approach the coast as a 1 or a 2 like Erin in 1995 did

As the NHC documented, its only those approaching the northern GOM as major hurricanes that weaken, which has me thinking that its a heat content issue

I was thinking the Same Derek..I think If Rita has not turned and went directly over Gal Bay she would have never weakened...I think as soon as the Nly component has commenced in the Gulf the closer to land the faster the decline...

[vbhoutex]

Finally, think of all the big Cat 5s of the past - all were moving to the W-WNW south of the Bermuda high. Ventillation is generally good south of the high, and wind shear is low. That would mean that the Texas coast may be at a higher risk of being hit by an intensifying major hurricane than the northern Gulf Coast.

I hadn't thought of that, but you may have a point there. YIKES!!!!!! I hope we don't ever find out!!!

[Dr. Jonah Rainwater]

Don't forget: Even though lately we've been seeing alot of surge damage from weakening behemoth Gulf monsters, and the examples of Dennis and Charley seem to tell us that a recently intensified hurricane will not carry nearly as much storm surge, Hurricane Audrey bombed from a Category 2 to a Category 4 only a few hours before making landfall, and brought a devastating 10-foot surge into Cameron, Louisiana.

[wxmann_91]

Not only is the shear too strong and Heat Content too low, there's just too much dry air. And it's not from the GOM. Think how strong extratropical systems draw in cold air from the north so the wraparound is usually snow. Well, a tropical system can also do that, expect, since its summer, it's usually dry continental air. The stronger the system the more dry air is drawn in, so technically, a stronger storm (like a Cat 5 Katrina or Cat 4 Ivan) would be more likely to rapidly weaken right before landfall than a weaker storm (like a Cat 3 Frederic or Cat 2 Georges). That also explains why the convective cloud tops weaken (thus also the winds), but the pressures remain relatively low. Only chance of minimal weakening right before landfall is a storm that moves WNW, or a very small storm that bombs as it hits the shelf.