TC Bertha

[HURAKAN]

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT FRI JUL 04 2008

...SPECIAL FEATURE....

TROPICAL STORM BERTHA CENTERED NEAR 14.2N 28.3W AT 0900 UTC OR
ABOUT 275 NM WSW OF THE CAPE VERDE ISLANDS MOVING WNW AT 12 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1002 MB. MAXIMUM SUSTAINED
WIND SPEED IS 40 KT WITH GUSTS TO 50 KT. SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT42 KNHC
FOR MORE DETAILS. BERTHA IS PULLING AWAY FROM THE CAPE VERDE
ISLANDS. LITTLE IMPACT WAS AFFECTED NEAR SAL ON THU AS SFC
REPORTS SHOW MAX WINDS JUST OVER 20 KT...A PRESSURE OF 1012 MB
AND VERY LITTLE RAINFALL. MORE OF AN IMPACT WAS LIKELY FELT OVER
THE SOUTHERN ISLANDS CLOSER TO THE CORE OF COMPACT BERTHA.
A LARGE BURST OF CONVECTION FORMED EARLIER THIS MORNING BUT IT
HAS SINCE DECREASED SOME WITH THE ESTIMATED LOW-LEVEL CENTER
NEAR THE S PORTION OF THE BLOW-UP. STILL...NUMEROUS MODERATE TO
STRONG CONVECTION IS WITHIN 150 NM N AND 30 NM S OF THE CENTER.
STRENGTHENING IS FORECAST IN THE SHORT TERM AS ATMOSPHERIC
CONDITIONS APPEAR FAVORABLE AND OCEANIC CONDITIONS ARE MARGINAL.

[cycloneye]

Impressive QuickScat pass around four hours ago.

[StormTracker]

A thing of beauty isn't she!!!




She still doesn't have her own floater yet!!!

[Derek Ortt]

IF YOU'RE LOOKING FOR A BERTHA FLOATER

http://www.nwhhc.com/satellite.html

I created this yesterday for Bertha

[KWT]

I have to admit thats really impressive image stormtracker, I'd guess around 45-50kts for that, maybe the higher end of the estimate. The stronger it can get now the better for Bertha over the next 48hrs as it continues to go over the lower heat content. I'm looking foward to seeing what it does when it gets back over 26C+ waters, evn if shear may increase shortly after.

[wxman57]

Morning, all. Just opened up GARP and was positioning the center. At first, I thought the NHC was way off on the position, as my eye was drawn to that big ball of convection. But when I looked more closely at the low cloud filaments I can see that the LLC is on the south side of the convection, almost exposed. So it may not be as healthy as it appears at first glance.

Oh, and I plotted Bertha's track on a chart of oceanic heat content with SST contours. It's moving over progressively cooler water until tomorrow afternoon. By Sunday night, it's back over 26+C SSTs but should be encountering increased shear:

[KWT]

Yep wxman it does look like the deep convection is on the NE side of the system, though you can see the LLC is still just about under the convection. Models do show however a 24hrs period between when it gets back over warmer waters and when the shear increases, I think Monday will be the day when we will see any primary peak.

[wxman57]

I also just measured a 3-hr motion of 320 deg at 15 kts. There's some margin for error as we can't really see the center, though. That blob of convection is definitely moving NW, though. Center looks to be near 15N/28.3W. That's pretty far north to have a shot at impacting the Caribbean from east of 30W.

Another calculation - from its current position it would have to track toward 273 degrees to clip the NE Caribbean.

Here's a close-up shot with 1-deg lat/lon lines. My cursor is near the estimated center. Note the closed-cell stratocumulus in its path, an indication of cool water.

[KWT]

wxman57 I think the Caribbean should be in the clear from this one even the models that take a very westerly track like the ECM still has this clearing Caribbean with room to spare.

Something thats far more possible is a Bermuda hit given the way the models are trending closer to the 60W line of longitude. Interestingly by the way the GFDL did have this heading at 313 degrees this morning which if wxman57 calculations are correct isn't far off the mark.
Aren't those clouds you highlight normally typical of stable airmasses?
If so then of course Bertha may have a hard time in the next 48hrs but then again that has been expected right since we had an invest on our hands.

[wxman57]

Here's the same shot with the NHC's 12Z position plotted on it (14.7N/29W). Center even farther from the convection:

[cycloneye]

57 your position also here.

AL, 02, 2008070412, , BEST, 0, 147N, 290W, 45, 1000, TS, 34, NEQ, 75, 30, 0, 75, 1012, 180, 30, 0, 0, L, 0, , 0, 0, BERTHA, D,

[HURAKAN]

The Caribbean is most likely in the clear. In 1996 Bertha crossesd the 15°N latitude line @ around 53°W. Bertha 2008 is doing it before reaching 30°W.

[cycloneye]

I agree 57 and Sandy,unless something surreal happens with the track,the NE Caribbean is going to be clear.

[wjs3]

wxman57 I think the Caribbean should be in the clear from this one even the models that take a very westerly track like the ECM still has this clearing Caribbean with room to spare.

Something thats far more possible is a Bermuda hit given the way the models are trending closer to the 60W line of longitude. Interestingly by the way the GFDL did have this heading at 313 degrees this morning which if wxman57 calculations are correct isn't far off the mark.
Aren't those clouds you highlight normally typical of stable airmasses?
If so then of course Bertha may have a hard time in the next 48hrs but then again that has been expected right since we had an invest on our hands.

Here's a link to a sample program from the Penn State University program that talks about open and closed cell convection. Yess, the closed cell Convection Chris pointed out is indicative of, among other things, stable air masses over cool waters.

http://www.worldcampus.psu.edu/accuweat ... H6782_1207

(PS--this was used as an advertisement for the program at AccuWeather.com--hence they appear in the link--but there's no relationship between the program and accuwx.)

[wxman57]

Another interesting shot showing the current location of the TUTT low and trof in Bertha's path. The low is forecast to move eastward with time, but the TUTT will trail southwestward into the NE Caribbean through 5 days. So once Bertha finally gets back over warmer water it'll be encountering the TUTT (shear). Might even turn sharply northward if it's better-organized. But since everything seems against strengthening, it could just be a weak TS or TD with an exposed center by then:

[KWT]

Yeah you can't miss that wxman57. I think this system will have a better chance if it take the more southerly route however because whilst it will get hit very hard by shear the duration of it wouldn't be nearly as long as it would be if it was to end up closer to the TUTT system, as the system would hit by two blows so to speak closer to the TUTT, by the tail and then by the TUTT's circulation as well.

The Caribbean should be fine I'd have thought, Bermuda however may have to watch a little closely.

[Thunder44]

I agree wxman57. Things don't seem to be see favorable for Bertha to strengthen very much on it's current path. That's why the new GFDL forecast for Cat 2 or 3 hurricane in 5 days is hard for me to believe. I think the chances are greater that it won't survive than becoming that strong SE of Bermuda.

[KWT]

There is actually some light shear on the system now, SHIPS does have it at 8kts which isn't much but I suppose under cool SST's may be something to try and deal with. Convection also still on the NE side.
I reckon Thunder that Bertha will hold steady at 40-45kts for the next few days, then depending on whether shear has ramped up or not it may have a small window to strengthen as it hits the warmer waters.
Its still got a good little structure to it for now, SST's drop to thier lowest in 12-24hrs time, the dmin today may be quite hard for this system...

Also I do wonder whether we will see recon tasked on this system in the next couple of days, Derek said in the other forum they can fly to 40W and if its a threat to Bermuda its quite possible.

[cycloneye]

The NHC floater is now up:

[Derek Ortt]

There is actually some light shear on the system now, SHIPS does have it at 8kts which isn't much but I suppose under cool SST's may be something to try and deal with. Convection also still on the NE side.
I reckon Thunder that Bertha will hold steady at 40-45kts for the next few days, then depending on whether shear has ramped up or not it may have a small window to strengthen as it hits the warmer waters.
Its still got a good little structure to it for now, SST's drop to thier lowest in 12-24hrs time, the dmin today may be quite hard for this system...

Also I do wonder whether we will see recon tasked on this system in the next couple of days, Derek said in the other forum they can fly to 40W and if its a threat to Bermuda its quite possible.

NOAA recon usually flies if there is a research mission, not based upon a threat to land. That is unless NHC tasks them, but I do not recall a tasking of NOAA for the open Atlantic