ATL: BERTHA - Post-Tropical - Discussion

[al78]

It is not every year the Atlantic has more named storms than the NW Pacific in May, in fact, it has more named storms than the whole Pacific ocean north of the equator so far!

[Shell Mound]

https://twitter.com/dylanfedericowx/status/1265638398414520320?s=21

Landfall occurred in the very same region that Hugo impacted back in 1989. Based on radar and buoy data, this was likely close to 55 knots / 1000 mb at landfall, given the formative eyewall, quick intensification, and small ROCI (radius of outermost closed isobar) embedded in high environmental pressures. Given that the peak sustained winds were registered outside the strongest convection, Bertha was almost certainly a bit stronger than the NHC currently indicates. Post-seasonal analysis may well nudge up both the time of formation and the peak/landfall intensity. Plus, bear in mind that Bertha made landfall in a very remote area, in and near the Francis Marion National Forest and Bulls Bay, SC, in which surface data are quite sparse.

 https://twitter.com/webberweather/status/1265624679118708736



 https://twitter.com/AndyHazelton/status/1265625049177952261



 https://twitter.com/pppapin/status/1265628375332184071

[TallyTracker]

Now a tropical depression.

...BERTHA WEAKENS TO A TROPICAL DEPRESSION...
...HEAVY RAINFALL SPREADING ACROSS THE CAROLINAS...


SUMMARY OF 200 PM EDT...1800 UTC...INFORMATION
----------------------------------------------
LOCATION...33.7N 80.2W
ABOUT 65 MI...105 KM NNW OF CHARLESTON SOUTH CAROLINA
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...NNW OR 330 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...1007 MB...29.74 INCHES

[FireRat]

Bertha really likes the Carolinas huh, getting her rains today here in NC, gonna be a wet night!

[galaxy401]

I completely slept on this storm because I thought it had no chance of developing. I guess I learned to never sleep on the Gulf Stream.

Bertha better not delay the upcoming astronaut launch. Edit: It did

[SconnieCane]

I don't know for sure, but with just 2 hours this has to be the one of the storms with the least amount of time between being named and making landfall, at least as far as I can remember.

Remember Imelda from last year? Made landfall mere hours after being named a 35-kt TS and drowned Beaumont in near-Harvey fashion.

[kevin]

I completely slept on this storm because I thought it had no chance of developing. I guess I learned to never sleep on the Gulf Stream.

Bertha better not delay the upcoming astronaut launch.

Unfortunately they announced that due to weather conditions the astronaut launch had to be postponed.

[Kalrany]

Wow, Humberto (2007) got KO'ed for fastest. That was 3 hours.

[HurricaneRyan]

Lmao what? An entire storm in the matter of 3 hours? Jesus

[Hypercane_Kyle]

FYI - Bertha's genesis was purely tropical. We've seen ULL aid in tropical wave's developments many time by enhancing convection, such as Rita in 2005. If the ULL had been over Bertha and worked its way to the surface, that would be a subtropical genesis.

[AJC3]

At the risk of wading into a subjective or semantic debate, here's my two cents concerning the genesis of Bertha.

1. The incipient disturbance that went on to become Bertha was purely tropical.
Looking back at the TWDATs from NHC and unified surface analyses, it is clear that the northern flank of an AEW (African Easterly Wave, or T-wave if you wish) over the northwestern Caribbean fractured and turned northward into the eastern GOMEX.

2. The genesis process was not purely tropical.
This was without a doubt a BE (baroclinically enhanced) system. Once it reached the SE GOMEX, there was protracted and significant amount of dynamic (non-tropical) mid and upper level forced ascent (H50 PVA/H25 divergence) on the east side of the large, negative-tilt, quasi-stationary upper trough which covered the GOMEX for a few days. This forcing generated convection, which in turn spawned several low to mid level vortices, and gradually lowered pressures at the surface, resulting in a broad, elonagted trough from the eastern GOMEX across Florida. Eventually, this forcing shifted offshore the Florida east coast. Once that occured, more significant convection developed in that area, especially over the Gulf Stream. This generated further lowering of pressures, which deformed/absorbed the weak LLC (one of a few) that had formed over the peninsula, just as it was about to move offshore around Daytona Beach. This new low pressure area, now separated from the trough to its west, was steered northward in between the upper trough to the west and the Atlantic ridge to the east. It quickly intensified into a TD/TS and then moved onshore the SC coast.

You can argue whether or not it would have formed without the upper forcing, I think it's more likely that it would not have, given the time of year, but it could be debated.

Anyway, as always...my 2 cents...YOMV

[Shell Mound]

Landfall highlight(s):
 https://twitter.com/EricBlake12/status/1265641487825543170

[HurricaneEnzo]

At the risk of wading into a subjective or semantic debate, here's my two cents concerning the genesis of Bertha.

1. The incipient disturbance that went on to become Bertha was purely tropical.
Looking back at the TWDATs from NHC and unified surface analyses, it is clear that the northern flank of an AEW (African Easterly Wave, or T-wave if you wish) over the northwestern Caribbean fractured and turned northward into the eastern GOMEX.

2. The genesis process was not purely tropical.
This was without a doubt a BE (baroclinically enhanced) system. Once the system reached the SE GOMEX, there was protracted and significant amount of dynamic (non-tropical) mid and upper level forced ascent (H50 PVA/H25 divergence) on the east side of the large, negative-tilt, quasi-stationary upper trough which covered the GOMEX for a few days. This forcing generated convection, which in turn spawned several low to mid level vortices, and gradually lowered pressures at the surface, resulting in a broad, elonagted trough from the eastern GOMEX across Florida. Eventually, this forcing shifted offshore the Florida east coast. Once that occured, more significant convection developed in that area, especially over the Gulf Stream. This generated further lowering of pressures, which deformed/absorbed the weak LLC (one of a few) that had formed over the peninsula, just as it was about to move offshore around Daytona Beach. This new low pressure area, now separated from the trough to its west, was steered northward in between the upper trough to the west and the Atlantic ridge to the east. It quickly intensified into a TD/TS and then moved onshore the SC coast.

You can argue whether or not it would have formed without the upper forcing, I think it's more likely that it would not have, given the time of year, but it could be debated.

Anyway, as always...my 2 cents...YOMV

That was my thinking you can't really say it was 'pure tropical' development. Not strictly non-tropical either the truth probably likes somewhere in the middle.

[TallyTracker]

At the risk of wading into a subjective or semantic debate, here's my two cents concerning the genesis of Bertha.

1. The incipient disturbance that went on to become Bertha was purely tropical.
Looking back at the TWDATs from NHC and unified surface analyses, it is clear that the northern flank of an AEW (African Easterly Wave, or T-wave if you wish) over the northwestern Caribbean fractured and turned northward into the eastern GOMEX.

2. The genesis process was not purely tropical.
This was without a doubt a BE (baroclinically enhanced) system. Once the system reached the SE GOMEX, there was protracted and significant amount of dynamic (non-tropical) mid and upper level forced ascent (H50 PVA/H25 divergence) on the east side of the large, negative-tilt, quasi-stationary upper trough which covered the GOMEX for a few days. This forcing generated convection, which in turn spawned several low to mid level vortices, and gradually lowered pressures at the surface, resulting in a broad, elonagted trough from the eastern GOMEX across Florida. Eventually, this forcing shifted offshore the Florida east coast. Once that occured, more significant convection developed in that area, especially over the Gulf Stream. This generated further lowering of pressures, which deformed/absorbed the weak LLC (one of a few) that had formed over the peninsula, just as it was about to move offshore around Daytona Beach. This new low pressure area, now separated from the trough to its west, was steered northward in between the upper trough to the west and the Atlantic ridge to the east. It quickly intensified into a TD/TS and then moved onshore the SC coast.

You can argue whether or not it would have formed without the upper forcing, I think it's more likely that it would not have, given the time of year, but it could be debated.

Anyway, as always...my 2 cents...YOMV

This is very helpful! Thanks for the detailed explanation! The genesis process seemed to be more complex than simply development of a tropical wave or purely of non-tropical origins.

[HurricaneBelle]

Bertha really likes the Carolinas huh, getting her rains today here in NC, gonna be a wet night!

Bertha ended up roughly following the path of Hugo after landfall, moving into the Charlotte area then up through West Virginia and Ohio moving west of north, a somewhat rare track at that latitude.