Do N moving hurricanes in the N GOM naturally weaken?

[tallywx]

All things being equal, shouldn't a northward moving hurricane of medium to large size making landfall on the northern Gulf coast naturally weaken? Assuming SSTs are constant across the entire Gulf, and upper-level conditions remain constant, shouldn't the fact alone that as a storm approaches the northern Gulf coast, the outer circulation pulls drier continental air from the north with less latent heat into the circulation, cause stabilization as that air works into the center and force weakening? A storm might not weaken per se if other conditions can overcome it, but isn't this drier air factor a constant negative factor that must always be overcome for this particular directionality and location of landfall?

One can see how a small storm would not weaken, because by the time this takes place the storm is almost onshore, but for storms with a larger circulation envelope that extend over land far before the eye crosses the shore, wouldn't this be a distinct possibility?

[tailgater]

I doubt it would may much of a difference unless it's moving very slow or on western end of the GOM.

[Brent]

I can't think of a northward moving one in recent years that DIDN'T weaken. Opal was almost a Cat 5 and was barely a 3 when it came inland. Lili went from a Solid 4 to a weak 2 in the few hours before landfall. Ivan was a 5 when it crossed Cuba and came in as a 3.

[SunnyThoughts]

Tally, your assumptions seem logical to me. I suppose it would depend on the size of the storm as you spoke of, and also the forward speed.

[Derek Ortt]

if everything remains constant (meaning no parameters change allowing for a decrease in SLP), ALL northward moving TC's will experience a spin downin the wind speed. The reason is that (f+zeta)/h remains constant and f increases with latitude. Zeta is the relative vorticity

[SouthernWx]

In September 1975, hurricane Eloise smashed into the Florida panhandle near Destin at peak intensity....955 mb and 110 kts, and was deepening to the time of landfall. Eloise isn't mentioned much on the internet, but caused severe damage to a then-sparsely populated "Miracle Strip" between Panama City Beach and Fort Walton Beach.

In September 1979, hurricane Frederic maintained a peak intensity of 130 mph the last 18-24 hours before landfall....and caused extensive damage from the Orange Beach/Gulf Shores, Alabama westwards to Pascagoula, Mississippi.

In August 1969, there is virtually no evidence that hurricane Camille weakened before landfall. In fact, if the final USAF recon vortex fix before landfall was accurate (918 mb), Camille deepened 9 mb during the final few hours before landfall, and all indications (WSR-57 radar, post storm survey, surface obs at Columbia, MS...well inland, etc) indicate an extremely violent and well developed hurricane at time of landfall.

[MGC]

Camille and Betsy?......MGC

[SouthernWx]

Camille and Betsy?......MGC

Betsy is another excellent example of a major hurricane which was stronger at landfall along the Gulf coast than when it struck south Florida; and was in fact, was near peak intensity when Louisiana landfall occurred (948 mb/ 115 kt IMO).

[MGC]

Again you are correct SouthernWx. Betsy did a good bit of intensifying just before landfall south of New Orleans. I am just worried that the trend of the last three major hurricanes that weakened in the N GOM will be viewed as the way it will be during future events and people we take that into consideration and not evacuate.....MGC

[Steve]

Each case is essentially different. In Louisiana, you often don't have any real land for several miles inland. It also depends into what the system is moving. If the steering currents are very weak with a jet stream pulled up far to the north, it's possible that you won't get any weakening until the storm is more or less inland (outside of frictional effects). Sometimes a storm will ride up a surface trof or even ahead of a front where there really isn't any dry air to pull in. That all changes the later in the season you go where (e.g. Juan 1995) a northward moving storm or one hanging out in the Northern Gulf can actually pull down the cold.

As for recent storms that did weaken:

Opal - Hit a nice warm SST pocket in the southern Gulf before turnnig off NE.

Lili - Crossed some stirred up water from Isidore a week or two prior which took away a lot of her juices.

Ivan - Ivan was still a bull, but he he had lost some of his punch. I'm not sure if he crossed any of the paths from the other storms or if that was all the Northern Gulf could have supported.

The thing to remember (ref. Gilbert) is that it takes a collossal amount of energy to maintain a storm at Cat 4 or Cat 5 (even Cat 3) status. The longer an IH exists, the greater the chance that it's going to level off.

Steve

[tallywx]

In September 1975, hurricane Eloise smashed into the Florida panhandle near Destin at peak intensity....955 mb and 110 kts, and was deepening to the time of landfall. Eloise isn't mentioned much on the internet, but caused severe damage to a then-sparsely populated "Miracle Strip" between Panama City Beach and Fort Walton Beach.

Eloise was an average-sized storm. Its cloud radius was about 100 miles in diameter. You're right in that it was a northward-moving storm that strenthened significantly close to the coast. The thing that caused it to strengthen was that it started interacting with a trough (notice in the best track that strengthen occurred right when the track bent more toward the north). Thus, one of the assumptions in my theory (that no other factors become more or less favorable) does not apply.

In September 1979, hurricane Frederic maintained a peak intensity of 130 mph the last 18-24 hours before landfall....and caused extensive damage from the Orange Beach/Gulf Shores, Alabama westwards to Pascagoula, Mississippi.

I have no argument against your Frederick example. It was an average-sized storm that strengthened across the entire basin with little apparent change in the "other factors."

image: http://www.csc.noaa.gov/products/alabama/htm/fred.htm

In August 1969, there is virtually no evidence that hurricane Camille weakened before landfall. In fact, if the final USAF recon vortex fix before landfall was accurate (918 mb), Camille deepened 9 mb during the final few hours before landfall, and all indications (WSR-57 radar, post storm survey, surface obs at Columbia, MS...well inland, etc) indicate an extremely violent and well developed hurricane at time of landfall.

Camille was smaller than average, and thus wasn't able to draw upon the continental air until it was virtually on land.

Camille and Betsy?......MGC

Betsy was moving toward the WNW at landfall and thus does not fall within my northward-moving theory.

[Steve]

Oops Juan was in 1985 not 1995.

Btw tally, it really depends. Sometimes north moving storms can actually wrap up at landfall mirroring the frictional effects often seen in Texas landfalls and kind of with Charley last year.

Steve

[HurricaneBill]

Remember, Lili and Opal strengthened quickly, but were rather disorganized Category 4s. I don't think it was a cold wake from Isidore that weakened Lili. I think it was dry air (which is lethal to a hurricane).

Plus, although Lili rapidly weakened, she did look like she was beginning to become more organized at landfall.

[Derek Ortt]

Lili was sheared like a chea-pet, as has been documented many times.

It was also the most disorganized cat 4 hurricane, EVER. Recon radar showed only about a 50% eye wall at peak intensity and hurricane force winds did not even extend to the SW quadrant

[BreinLa]

Ohhhh sheared like a chea pet is that what pissed her off. She was mad enough to tear my fence up and knock my favorite tree down. Still pissed at Lili Lol

[dhweather]

IIRC, Lili, Ivan, Opal, and others all came into shear as they approached
land.

I don't think there's much correlation into moving due north and weakening. Timing is everything, and if there are westerlies further
north (as was with Ivan), then it's gonna happen. If not, talk to
Camille, Frederick, and others.

[Stormsfury]

Each case is essentially different. In Louisiana, you often don't have any real land for several miles inland. It also depends into what the system is moving. If the steering currents are very weak with a jet stream pulled up far to the north, it's possible that you won't get any weakening until the storm is more or less inland (outside of frictional effects). Sometimes a storm will ride up a surface trof or even ahead of a front where there really isn't any dry air to pull in. That all changes the later in the season you go where (e.g. Juan 1995) a northward moving storm or one hanging out in the Northern Gulf can actually pull down the cold.

As for recent storms that did weaken:

Opal - Hit a nice warm SST pocket in the southern Gulf before turnnig off NE.

Lili - Crossed some stirred up water from Isidore a week or two prior which took away a lot of her juices.

Ivan - Ivan was still a bull, but he he had lost some of his punch. I'm not sure if he crossed any of the paths from the other storms or if that was all the Northern Gulf could have supported.

The thing to remember (ref. Gilbert) is that it takes a collossal amount of energy to maintain a storm at Cat 4 or Cat 5 (even Cat 3) status. The longer an IH exists, the greater the chance that it's going to level off.

Steve

Good post, Steve.

In Opal's case, Opal crossed an area of very warm SST's in the Eastern Gulf (an area where the Gulf Stream originates) ... furthermore, the storm was picked up by a trough, in which divergence aloft enhanced development substantially ... RECON noted an unusually large amount of CG strikes during that mission (very intense thunderstorms around the core), which is very unusual for a hurricane. Now, remember it takes a substantial deep pool of warm SST's to maintain a hurricane, let alone an intense hurricane, and as Opal approached the Fla Panhandle, waters were cooler, but also very shallow (less than 50M for 26C SST's).

Ivan did get near some of Frances' upwelling but again, see Opal's reasoning ... Ivan had been so intense for so long that at some point, some kind of eyewall replacement cycle had to occur. Again, the shallower waters near the coast can make it a bit difficult for IH's to maintain themselves ...

Lili had a lot of different things destroy its intensity... the primary reason was an upper level low in SE TX interacting and choking the western portion of the outflow so badly that Lili basically self-destructed.. It also was undergoing an eyewall replacement cycle, which it had no opportunity to recover from.

In the cases of Camille and Betsy, landfall points were further west and during AUGUST/Early September ... SST's in the GOM especially near the coast can approach 90º during this portion of the summertime and even shallower SST depths don't mean squat during that timeframe. So for obvious reasons, with conditions primed for development and SST's more than able to sustain and further develop an intense storm, it just happened that with these particular storms, they began RIC's at the wrong time.

SF

[HurricaneBill]

Lili was sheared like a chea-pet, as has been documented many times.

It was also the most disorganized cat 4 hurricane, EVER. Recon radar showed only about a 50% eye wall at peak intensity and hurricane force winds did not even extend to the SW quadrant

What was Opal's eye like?

(Yes, Opal did have an eye.)

[AL Chili Pepper]

In '79, Frederic had a rise in barometic pressure prior to landfall. Shortly before crossing the coast, the pressure dropped back to 946mb. I remember the geek on the radio talking about a double eyewall. That makes me wonder whether Frederic was completing an eyewall replacement. Wish I had my internet DSL back then.

12 GMT 9/12/79 27.4N 87.0W 135 943 Category 4 Hurricane
18 GMT 9/12/79 28.4N 87.7W 135 950 Category 4 Hurricane
0 GMT 9/13/79 29.7N 88.0W 135 946 Category 4 Hurricane

[Anonymous]

Notice, many of the weakening hurricanes occur in September. August tends to be a deadly time. However, it's only a matter of time before Camille occurs again.