Atlantic Tropical Action 2014

[hawkeye_wx]

I can't imagine this thing is still a tropical cyclone.  The visible loop strongly suggests an open wave.

[jcwxguy]

so she opened up into a wave

[phil882]

Apologies for the long post, but Its really quite fascinating what happened this morning. When the surface circulation is fragile, it doesn't take much to destroy it, and it appears that cold downdrafts resulting from convective activity this morning destroyed of the surface circulation. Check out this long radar animation from Brian McNoldy.

 

 

Lets break down what happens here. There is still a distinct low-level circulation you can identify on radar up to around 1200 UTC. Beyond that you see convection go up in bands around the circulation, but collapses near the center by around 1400 UTC.

 

In a healthy TC this convection would not entrain as much dry air, because the profile would be close to moist adiabatic in the inner core, and WISHE would continue to feed the updraft as long as the SSTs were sufficient. This requires deep moist inflow that results in high boundary layer theta-e in the inner core of the TC via surface heat fluxes from the ocean into the atmosphere. 

 

In a sheared TC in proximity to dry air, dry air entrained into the convective cloud will weaken the updraft and enhance the downdraft. If the downdraft reaches the surface, that air could spread outward and disrupt a weak TC with a weak pressure gradient from the environment. That's why arc clouds tend to be a detriment for TC organization and development, since the arc clouds are simply outflow boundaries that are propagating away from the convection that collapses beforehand. This outflow transports lower theta-e air originating in the downdraft (theta-e is relatively low in the mid-levels) to the surface. The surface circulation then must do more work via SHF and LHF to restore the theta-e profile at the surface, which takes time. 

 

The important thing to remember though is a TC circulation has a certain amount of resiliency due to inertial stability arguments. Stronger TCs have more inertial stability so things like outflow boundaries and advection of lower theta-e into the storm core does have a large of a detrimental effect. Sure the storm might weaken and become disorganized, but the surface circulation remains intact and will reorganize as it tries to mix out the negative environmental influences. 

 

When that TC is weak though, things like a larger cluster of thunderstorms collapsing in the inner core can destroy the circulation. Bertha had a more vigorous circulation yesterday, so even as these things were happening, the circulation wasn't destroyed, just battered as it attempted to reorganize.

 

That's the catch 22 with sheared TCs in low moisture environments. Convection is always pulsing, and sometimes that convection has a negative effect to the storm structure. In some cases it can cause a TC circulation to spin down faster than if no convection existed (due to the dry downdrafts disrupting the circulation). That's probably what happened this morning. 

[Hailstoned]

From Rincon, P.R.: "Height" of Bertha seems about now w/darkly overcast skies, light to moderate rains and

Intermittent rolls of thunder. The wind is occasionally gusty to ~20 mph.

But what the heck; encountering a Cape Verdean system in the tropics, even if only a weak sister of one, is worthwhile.

[phil882]

Bertha is looking halfway decent on IR imagery this evening... just too bad it doesn't really have a surface circulation according to recon though. 

[hawkeye_wx]

The first visible loop this morning suggests Bertha has a good shot at organizing again.  The upper level flow is still not great, but it is less unfavorable this morning compared to the last couple mornings.  It should only improve further the next couple days.  The convection is showing decent organization over the eastern half of the circulation.  I think all models are forecasting intensification as it heads for the recurve.

[Superstorm93]

Should finally be able to organize again.

 

Recon isn't transmitting data ATM, so not really sure what its doing. 

 

[bluewave]

Bertha is continuing the pattern of recent years where the more favorable

area for strengthening is north of the tropics.

 

 

 

 

 

 

 

 

[Superstorm93]

[TropicalAnalystwx13]

Surface winds of 50 mph to the southeast of the center. Slow intensification looks to have commenced.

[LongBeachSurfFreak]

Surface winds of 50 mph to the southeast of the center. Slow intensification looks to have commenced.

Excellent! Bertha is on track to send most of the east coast a couple of days of fun waves without anything in the damaging range.

[AvantHiatus]

Excellent! Bertha is on track to send most of the east coast a couple of days of fun waves without anything in the damaging range.

The high-resolution models have been consistently closer to the coast, coming within 250 NM of NJ and nearly landfalling on OBX. Here are the 12z GFS ensembles, which have dramatically shifted westward.

 

[LongBeachSurfFreak]

The high-resolution models have been consistently closer to the coast, coming within 250 NM of NJ and nearly landfalling on OBX. Here are the 12z GFS ensembles, which have dramatically shifted westward.

That's pretty much optimal wave wise. The only limiting factor is size and strength. Bill is the modern bench mark for swell size and that was a beast of a storm. It actually did a good amount of damage to the beaches here in New York and under sunny sky's. Bill had wave face heights in the 15-20 foot range. This looks to be more of a fun 3-6 foot type swell from obx north.

[AvantHiatus]

That's pretty much optimal wave wise. The only limiting factor is size and strength. Bill is the modern bench mark for swell size and the was a beast of a storm. It actually did a good amount of damage to the beaches here in New York and under sunny sky's. Bill had wave face heights in the 15-20 foot range. This looks to be more of a fun 3-6 foot type swell from obx north.

Looks pretty good atm, NHC calling for a Category 1 peak at 40N. Either way should be interesting to track.

[IsentropicLift]

The GGEM ensemble mean is about 75 miles southeast of the BM. Looks like a few close calls amongst the members.

[AvantHiatus]

The GGEM ensemble mean is about 75 miles southeast of the BM. Looks like a few close calls amongst the members.

The operational attempts a semi-fujiwhara effect. A secondary tropical cyclone forms offshore near the Grand Strand.

[Eyewall2005]

words aren't enough how tired its getting to watch these ugly sheared systems. Hoping these season has something interesting to give.

[AvantHiatus]

words aren't enough how tired its getting to watch these ugly sheared systems. Hoping these season has something interesting to give.

Looks like it's entering the window of opportunity, after passing out of the hostile tropics.

[phil882]

Yea Bertha looks worlds better than it did yesterday, when it technically wasn't really a tropical cyclone with a closed circulation. As long as the disturbance to its west doesn't impart significant shear over Bertha, it has a 24-48 hour window for significant intensification under warm waters. I like the NHC's forecast right now.

 

It will be interesting, however, to see the ECMWF, which has performed well with Bertha since genesis, continues to advertise Bertha being absorbed by the disturbance to the west. There might be some minor interaction between the two systems over the next 24-48 hours. 

[wxmeddler]

Low level AF recon just came out with good pressure/wind center. The NOAA plane had a dropsonde in the NE quad that splashed at 58kts. Impressive work today by Bertha.

[Superstorm93]

Up to 50 knots per delayed ATCF 

 

03L BERTHA 140804 0000 24.1N 73.0W ATL 50 1007

 

[tmagan]

Looking at this and thought it is unfortunate that the Bahamas do not have a series of functioning weather radars.

[Kory]

Unflagged 57 kt winds...doesn't look rain contaminated.  

[wxmeddler]

Pressure field is pretty tight for a central pressure of 1006 ish. 1016mb 60 miles away in the NE Quad.

[wxmeddler]

"Eyewall" dropsonde reported 54kts at splash with 68kts at 90m asl.

[phil882]

Only concerning thing from an intensification standpoint is the appearance that the low-level circulation is running away from the convection in the eastern and southern quadrant. Northwesterly shear might not be soon to give way if the system to its west continues to produce deep convection. The most recent runs of the HRRR have been suggesting that Bertha might run away from the current convective plume over the center, so keep an eye on it. 

 

[phil882]

I am also not sure why the NHC dropped the system over FL, it's been slowly getting better organized today. Perhaps they thought that Bertha would be the dominant system. 

 

[WxFreak11]

What happens if this system over Florida absorbs Bertha? Would this be tropical?

[phil882]

What happens if this system over Florida absorbs Bertha? Would this be tropical?

 

While pretty unlikely right now given Bertha's intensity, the resulting merger of the two systems would probably be tropical considering they are both warm core disturbances right now (although the system over FL right now is tangled up in a frontal boundary and the NHC might say the system has frontal characteristics). 

[WxFreak11]

Thanks Phil. Bertha has been a fun storm to track.