ATL: DANNY - Remnants - Discussion

[AJC3]

I just went back through the last 10 days, the windshear axis across the eastern Caribbean has been present just about every day, I never bought the idea from the models that the shear axis is going to move out of the way as Danny approaches the Islands.

That's the semi-permanent mid oceanic trough. It's an the upper tropospheric feature (hence, why it's call the TUTT), and it's position and strength both do fluctuate. On occasion, as I alluded to in a post from a few days ago, pieces of vorticity fracture off of the trough, and generally retrograde toward the W or SW. Its evolution over the course of a season is pretty fascinating to watch on water vapor imagery, especially with vapor-derived winds overlaid.

[OuterBanker]

Question. All the moisture off the seus appears to be headed se towards the carib and the mdr. It's quite evident on WV loops. The gap between the dry air and the moist sw atlantic is getting more narrow. Will this have any affect on Danny if the moisture arrives before Danny?

[AJC3]

Question. All the moisture off the seus appears to be headed se towards the carib and the mdr. It's quite evident on WV loops. The gap between the dry air and the moist sw atlantic is getting more narrow. Will this have any affect on Danny if the moisture arrives before Danny?

No, and here's why. Water vapor imagery primarily depicts upper tropospheric features. There is almost no information depicted below 600 MB on the water vapor (6.5 to 6.9UM) channel. The amount of potential moisture/water vapor within the lower troposphere is far greater than that aloft. It takes much higher moisture content for the lower levels to reach their saturation point than aloft, simply because the it's much colder aloft.

From what I see on the imagery, most of that moisture is from a combination jet cirrus/cirrostratus and thunderstorm blowoff.

Finally, we're still taking about 7-10 days out. The mid and upper level pattern will be quite different by then.

[Gustywind]

Tropical Storm Danny May Become a Hurricane Later This Week; Potential Threat to Lesser Antilles Next Week

Published Aug 19 2015 04:40 PM EDT


weather.com

http://www.weather.com/storms/hurricane ... antic-2015

•Tropical Storm Danny was located about 1,325 miles east of the Windward Islands in the eastern Atlantic Ocean as of 5 p.m. EDT Wednesday.
•Maximum sustained winds remained at 50 mph with higher gusts.
•The tropical storm is forecast to steadily strengthen as it moves west-northwest over the next several days. Danny is forecast to become a hurricane later this week.
•It will be until early next week before Danny reaches the longitude of the Lesser Antilles.


Tropical Storm Danny continues to spin about halfway between Africa and the Lesser Antilles in the central Atlantic Ocean.

Satellite imagery on Wednesday afternoon shows that Danny has a well-defined circulation center, though organized shower and thunderstorm activity near this center has been fairly limited. That said, we have recently observed a small flare-up of thunderstorms that we will be monitoring to see if they persist and/or expand, which would be a sign of increased organization.

The lack of organized thunderstorm activity may be due to some dry air being ingested by Danny, as noted by hurricane specialist Dr. Greg Postel of The Weather Channel. Dry air hampers tropical cyclones by encouraging the development of stronger thunderstorm downdrafts, which then either squelch nearby thunderstorms from forming or push them away.

This dry air is also stable, meaning it suppresses upward vertical columns of air needed to maintain or form new thunderstorms.

This will be a continual challenge to Danny over the next several days, as water vapor imagery indicates an ample reservoir of dry air north of Danny extending westward into the eastern Caribbean Sea.

Wind shear, namely, the change in wind speed with height either in speed and/or direction, can blow convection away from the center from a tropical cyclone. If strong enough, this can rip apart existing tropical cyclones.

Despite what had been a rather hostile atmosphere featuring record mid-July through mid-August Caribbean wind shear, Danny sits far south to remain in an environment of rather light wind shear.

So, assuming the atmosphere immediately surrounding Danny remains somewhat moist, Danny is forecast to strengthen to the first hurricane of the 2015 Atlantic hurricane season possibly as soon as Thursday night or Friday.
The movement of this system will be to the west-northwest the next few days. Computer model forecast guidance shows that it may not reach the longitude near the eastern Caribbean Sea (about 60 degrees West longitude) until early next week.


As a result, we have plenty of time to monitor its progress.

Given the aforementioned dry air and wind shear in place over the eastern Caribbean Sea, it's possible that this system eventually weakens once it reaches the vicinity of the Lesser Antilles.

In summary, it's far too early to know if this system will bring any significant impacts to those islands in the long-term future. Interests in the Lesser Antilles, the Virgin Islands and Puerto Rico should monitor the progress of Danny.

Stay tuned to The Weather Channel and check back with weather.com for updates on this system.

[Hammy]

Hopefully we can get a scatterometer and microwave pass overnight, if this is in fact turning into a stronger but smaller system we'll be able to get a more accurate feel on the intensity.

[northjaxpro]

http://199.9.2.143/tcdat/tc15/ATL/04L.DANNY/tc_ssmis/color/2degreeticks/20150819.2105.f19.x.colorpct_91h_91v.04LDANNY.45kts-1000mb-114N-415W.92pc.jpg

Danny trying to form a very small, tight inner core.

Wonder if this is the start of it tightening up and becoming a smaller system?

Danny always has had a small, well developed inner core since its classification to TS yesterday. Dry air just got ingested within the circulation the past 24 hours. However, deep convection is beginning to build back directly over that inner core right now.

[OuterBanker]

Thanks wxman for the explanation.

[Gustywind]

http://199.9.2.143/tcdat/tc15/ATL/04L.DANNY/tc_ssmis/color/2degreeticks/20150819.2105.f19.x.colorpct_91h_91v.04LDANNY.45kts-1000mb-114N-415W.92pc.jpg

Danny trying to form a very small, tight inner core.

Wonder if this is the start of it tightening up and becoming a smaller system?

Danny always has had a small, well developed inner core since its classification to TS yesterday. Dry air just got ingested within the circulation the past 24 hours. However, deep convection is beginning to build back directly over that inner core right now.

Agree with these shy bursts, but let's see if this trend continue or not. If these bursts can flaring up Danny could make a possible comeback. And that's why i advice all the islanders in the EC to be on their guard during the next couple of days. The big mistake for us is to neglect a poor appareance TS 50 mph sustained winds lacking convection with a vigorous circulation!

[northjaxpro]

You are right gustywind. Everyone in the Islands should never let their guard down anytime, but especially now with Danny. Danny is still a respectable TS currently with a very vigorous and well developed inner core. It is the reason why satellite appearance is not everything in showing how a storm is doing. In fact, satellite imagery can be deceptive at times, giving thought to some that it was weakening earlier today.

Meanwhile, deeper red convective tops now firing around the center. If this trend continues, pressures should start to fall off again and some strengthening will take place soon.

[blp]

Great article about CCKW and how it helped Danny.

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=3078

[Gustywind]

:uarrow: You are right gustywind. Everyone in the Islands should never let their guard down anytime, but especially now with Danny. Danny is still a respectable TS currently with a very vigorous and well developed inner core. It is the reason why satellite appearance is not everything in showing how a storm is doing. In fact, satellite imagery can be deceptive at times.

Meanwhile, deeper red convective tops now firing around the center. If this trend continues, pressures should start to fall off again and some strengthening will take place soon.

Nice and bright analysis! Danny has surely others things in store as many of the others TS of the past, today is day of rest after the crazy tuesday in terms of energy. Hopefuly, there's SAL in vicinity but imagine the contrary! I repeat again, we want some water but we don't want any cane!!!

[Gustywind]

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT WED AUG 19 2015


...SPECIAL FEATURES...

TROPICAL STORM DANNY CENTERED NEAR 11.5N 42.0W AT 19/2100 UTC OR
1151 NM E OF THE LESSER ANTILLES MOVING W AT 9 KT. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 1000 MB. MAXIMUM SUSTAINED WIND
SPEED IS 45 KT WITH GUSTS TO 55 KT. SCATTERED MODERATE AND
ISOLATED STRONG CONVECTION IS MAINLY CONFINED TO THE NW HALF OF
THE STORM WITHIN 120 NM IN THE NW SEMICIRCLE. THE OFFICIAL
FORECAST IS FOR DANNY TO STRENGTHEN TO A HURRICANE BY 48 HOURS
AS IT MOVES TO THE W-NW AT A SLIGHTLY SLOWER FORWARD SPEED. SEE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS.

[Hammy]

:uarrow: You are right gustywind. Everyone in the Islands should never let their guard down anytime, but especially now with Danny. Danny is still a respectable TS currently with a very vigorous and well developed inner core. It is the reason why satellite appearance is not everything in showing how a storm is doing. In fact, satellite imagery can be deceptive at times, giving thought to some that it was weakening earlier today.

Meanwhile, deeper red convective tops now firing around the center. If this trend continues, pressures should start to fall off again and some strengthening will take place soon.

Its looking good right now, but I've been skeptical from the start and will remain so until it can maintain this level of convection for about 12 hours or so--remember, it was not too longer after this point last night that the convection began to collapse.

[northjaxpro]

Well Hammy you are right. However, the difference tonight is that convection compared to this time last night is on the increase, and Danny appears for the moment to be at least mixing out the dry air around its inner core. We shall see if the convection maintains through the overnight. The structure of this system is why NHC kept Danny still a respectable tropical cyclone through its forecast cycle, well at least for the next 72 hours.

Tomorrow will be an interesting day to see if Danny can hold its convection around its inner core because if he does, he will at least attain Cat 1 status within the next 24 hours imo.

[NDG]

Great article about CCKW and how it helped Danny.

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=3078

Great article indeed!!!

I found this paragraph very interesting:

Fairly soon, Danny will encounter the more suppressed environment well behind the CCKW, together with the likelihood of higher wind shear and drier air favored by the ongoing El Niño regime. “I’ve seen a lot of cases where a mature tropical cyclone gets run over by the suppression behind a CCKW,” said Ventrice. “Can the hurricane create its own environment to protect itself from this?” One thing is for sure: the more latitude Danny gains, the less it will be influenced—for better or worse—by this CCKW. Meanwhile, it’s possible that the CCKW that gave Danny a boost will go on during the next week to favor development of another one or two easterly waves now over Africa, as suggested by some long-range model runs. After that, said Ventrice, “it doesn’t look like there’ll be much in the way of CCKW activity over the next two weeks.”

[Nimbus]

Looked to me like the deeper convection was being displaced north a little from the low level center.
Just doesn't look well stacked yet.

It usually takes a stronger system to pull down those mid latitude troughs.
If Danny continues weak and west much longer they are going to have to shift the tracks left again.

[Ntxw]

Great article about CCKW and how it helped Danny.

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=3078

Great article indeed!!!

I found this paragraph very interesting:

Fairly soon, Danny will encounter the more suppressed environment well behind the CCKW, together with the likelihood of higher wind shear and drier air favored by the ongoing El Niño regime. “I’ve seen a lot of cases where a mature tropical cyclone gets run over by the suppression behind a CCKW,” said Ventrice. “Can the hurricane create its own environment to protect itself from this?” One thing is for sure: the more latitude Danny gains, the less it will be influenced—for better or worse—by this CCKW. Meanwhile, it’s possible that the CCKW that gave Danny a boost will go on during the next week to favor development of another one or two easterly waves now over Africa, as suggested by some long-range model runs. After that, said Ventrice, “it doesn’t look like there’ll be much in the way of CCKW activity over the next two weeks.”

He is among the best in this field. CCKW's are interesting to follow, we know the MJO has influences weeks at a time but this stuff in the short term span his research in it has shown they can influence in hours and days.

His U Albany hosted site has great stuff if you want to follow CCKW's. Blue's are rising motion phases, while hot colors are sinking motion or suppressed phase.

[CrazyC83]

:uarrow: You are right gustywind. Everyone in the Islands should never let their guard down anytime, but especially now with Danny. Danny is still a respectable TS currently with a very vigorous and well developed inner core. It is the reason why satellite appearance is not everything in showing how a storm is doing. In fact, satellite imagery can be deceptive at times, giving thought to some that it was weakening earlier today.

Meanwhile, deeper red convective tops now firing around the center. If this trend continues, pressures should start to fall off again and some strengthening will take place soon.

With the well defined inner core, all it would take is a good 24 hours and it could quickly enter an RI'ing phase. We need to be on guard for that...

[blp]

Great article about CCKW and how it helped Danny.

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=3078

Great article indeed!!!

I found this paragraph very interesting:

Fairly soon, Danny will encounter the more suppressed environment well behind the CCKW, together with the likelihood of higher wind shear and drier air favored by the ongoing El Niño regime. “I’ve seen a lot of cases where a mature tropical cyclone gets run over by the suppression behind a CCKW,” said Ventrice. “Can the hurricane create its own environment to protect itself from this?” One thing is for sure: the more latitude Danny gains, the less it will be influenced—for better or worse—by this CCKW. Meanwhile, it’s possible that the CCKW that gave Danny a boost will go on during the next week to favor development of another one or two easterly waves now over Africa, as suggested by some long-range model runs. After that, said Ventrice, “it doesn’t look like there’ll be much in the way of CCKW activity over the next two weeks.”

I agree that was a great tip.

[CrazyC83]

20150819 2345 11.9 42.3 T3.0/3.0 04L DANNY

Based on that combined with the higher winds than Dvorak reported yesterday, I would at least go up to 50 kt.