ATL: DORIAN - Post-Tropical - Discussion

[ozonepete]

Yeah so we always need to keep watching. I did a little annotation of a recent satellite image to explain how Dorian could strengthen because of the TUTT even though many people think a TUTT is always bad for a TC.

[Kingarabian]

DMAX isn't too far away so that could help it.

[chaser1]

Something looks oddly strange about the upper air. The "Artist Formerly Known as Dorian" is presently feeling some decent outflow and the strong shear to its west is evident on satellite. Long loop appears to be retrograding the shear in advance of Dorian's westward motion.

The strange part of it all, is when looking at the 0Z GFS, those 30 knot southerly winds at 200mb, suddenly go "POOF" in about 24-36 hours, and basically appears to have a weak anticyclone appear in its place just north of Hispanola??? During all this, the east coast trough is pulling out and the 500mb steering over and north of the Bahamas starts backing to the east around 72+ hours. Looks like SST's increasing if/when Dorian moves close to the S.E. most Bahamas/Turks.

UK Model from 0Z appears to redevelop Dorian as a Depression (or T.S.) in the Florida Straits and carry it over Key West moving NNW in the E. Gulf

[Hurricane Alexis]

Something looks oddly strange about the upper air. The "Artist Formerly Known as Dorian" is presently feeling some decent outflow and the strong shear to its west is evident on satellite. Long loop appears to be retrograding the shear in advance of Dorian's westward motion.

The strange part of it all, is when looking at the 0Z GFS, those 30 knot southerly winds at 200mb, suddenly go "POOF" in about 24-36 hours, and basically appears to have a weak anticyclone appear in its place just north of Hispanola??? During all this, the east coast trough is pulling out and the 500mb steering over and north of the Bahamas starts backing to the east around 72+ hours. Looks like SST's increasing if/when Dorian moves close to the S.E. most Bahamas/Turks.

UK Model from 0Z appears to redevelop Dorian as a Depression (or T.S.) in the Florida Straits and carry it over Key West moving NNW in the E. Gulf

I've noticed the shear moving west as well. It was supposed to be experiencing 30kts of shear and it's not and it doesn't look like it will today either with the TUTT retrograding west.

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[chaser1]

:uarrow: Yeah so we always need to keep watching. I did a little annotation of a recent satellite image to explain how Dorian could strengthen because of the TUTT even though many people think a TUTT is always bad for a TC.

Funny, just read your recent prior posts as well. While I've seen how an upper low (or TUTT in this case) can help provide an outflow channel providing not too strong, did you happen to see the 0Z 200mb and how the TUTT pretty much vanishes only to be replaced with light anticyclonic conditions?? If this thing keeps firing, than I think something's up and the S.E. Bahamas need anticipate some squally weather at the least in about 2-3 days.

[ozonepete]

Something looks oddly strange about the upper air. The "Artist Formerly Known as Dorian" is presently feeling some decent outflow and the strong shear to its west is evident on satellite. Long loop appears to be retrograding the shear in advance of Dorian's westward motion.

The strange part of it all, is when looking at the 0Z GFS, those 30 knot southerly winds at 200mb, suddenly go "POOF" in about 24-36 hours, and basically appears to have a weak anticyclone appear in its place just north of Hispanola??? During all this, the east coast trough is pulling out and the 500mb steering over and north of the Bahamas starts backing to the east around 72+ hours. Looks like SST's increasing if/when Dorian moves close to the S.E. most Bahamas/Turks.

UK Model from 0Z appears to redevelop Dorian as a Depression (or T.S.) in the Florida Straits and carry it over Key West moving NNW in the E. Gulf

My worry is that the TUTT and its low will retrograde and weaken more quickly. This could allow something stronger than a TD or TS to go through there. I still don't think that will happen but I would certainly watch this until it dissipates.

[ozonepete]

DMAX isn't too far away so that could help it.

Actually DMAX is pretty much over. The sun is starting to rise now. What will be interesting, and not good news for the Bahamas and southern Florida, is if these "remnants of Dorian" keep strengthening even though DMAX is done. That would be another sign that the TUTT is weakening and retrograding...

[chaser1]

[b]Something looks oddly strange about the upper air. The "Artist Formerly Known as Dorian" is presently feeling some decent outflow and the strong shear to its west is evident on satellite. Long loop appears to be retrograding the shear in advance of Dorian's westward motion.

My worry is that the TUTT and its low will retrograde and weaken more quickly. This could allow something stronger than a TD or TS to go through there. I still don't think that will happen but I would certainly watch this until it dissipates.

Yeah was thinking the same thing, but didn't want to be the one to even say it.... Dorian has strangely maintained a significant amount of vorticity in light of shear and especially dry air up to this point. Unless he soon dissipates, than the way I see it nearly all conditions will turn significantly more favorable by 48 hours (or sooner). Am still scratching my head regarding how quickly the upper air would be appearing to transition just north of the islands.

[beoumont]

Actually, in maybe a majority of cases of tropical cyclone genesis there is a cold low in "the general vicinity". Of course it has to be out in front of the easterly wave or tropical disturbance and either retrograding faster than the wave, diving SW in front of (the cut off low shot across the bow scenario), or collapsing completely (the collapsing low theory / scenario).

The shot-across-the-bow sequence, I have observed, can be the most potent. A low cuts off from the NE-SW oriented trough (tutt), dives SW in front of the wave or disturbance, and continues SWward away from the wave, causing ridging to take place in its wake between the cut-off and the parent upper level trough.

It is often this relative close proximity to the tutt-tutt that sets off convection in the first place-place.

[Kingarabian]

DMAX isn't too far away so that could help it.

Actually DMAX is pretty much over. The sun is starting to rise now. What will be interesting, and not good news for the Bahamas and southern Florida, is if these "remnants of Dorian" keep strengthening even though DMAX is done. That would be another sign that the TUTT is weakening and retrograding...

Sorry man. How long does DMAX last?

[chaser1]

Um, yeah.... looking like the latter. Now clearly seeing the shrinking (and warming) ULL around 25N & 70W retrograding WNW and away. Shear zone directly ahead of Dorian also retrograding, but seemingly becoming less strong; And according the maps, would appear to transition into the western side of a more broad anticyclonic upper ridge that pretty much "evolves" over Dorian (or Erin-Daughter of Dorian)

[bahamaswx]

Looks to be done expanding. We'll see how long the convection maintains.

[chaser1]

....and the BEST part is that it was the mighty NAM model that was closest to sniffing it out-crazy!

[ozonepete]

DMAX isn't too far away so that could help it.

Actually DMAX is pretty much over. The sun is starting to rise now. What will be interesting, and not good news for the Bahamas and southern Florida, is if these "remnants of Dorian" keep strengthening even though DMAX is done. That would be another sign that the TUTT is weakening and retrograding...

Sorry man. How long does DMAX last?

All is well my friend. You are in a far away time zone. Love discussing these things with you. DMAX usually starts a few hours after sunset and maxes 1 or 2 hours before sun-up. DMIN starts a few hours after sunrise and hits its minimum 1 or 2 hours before sunset. So I have to hit the hay now but if you'll be watching look to see if convection maintains for a few hours after sunrise there (6 AM EDT). That would mean other factors (such as TUTT weakening) are allowing this to redevelop. I'm really not convinced that Dorian is done after tonight's flare-up and the seeming retrogression of the TUTT.

[JGrin87]

Anyone have a link to microwave imagery?

[beoumont]

The NAM is most bullish on an upper ridge; but we know how often the NAM verifies.

[chaser1]

Looks to be done expanding. We'll see how long the convection maintains.

Well, better get my 5 hours of "shut-eye" in; might be an interesting 2nd half of the day. I would'nt be surprised to again see Dorian's convection sheared some today, but given that the shear seems to be retrograding as well, perhaps out of the dryer stable air, and the already warmer sea surface temps., I would guess that there would not be too much further disrupted convection. I noticed something looking at the shortwave satellite loop, that hints of some evidence of possible low level banding trying to re-establish on the systems west side. Of course any hot towers that might go up would still likely be sheared off to the north. Point is however, this would be a likely tell-tale sign of increase convergence and the upward spiraling air aided some existent spin that remains in the low to mid levels.

[chaser1]

The NAM is most bullish on an upper ridge; but we know how often the NAM verifies.

IF that verifies, they'll be T.S. Warnings in affect for the Central Bahamas and South Florida in a couple days.

[beoumont]

jgrin 87 wrote: anyone have link to microwave imagery

http://tropic.ssec.wisc.edu/real-time/mimic-tc/2013_04L/webManagerIR/mainpage.html

[Gustywind]

000
AXNT20 KNHC 281041
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT SUN JUL 28 2013

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF
SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM THE
EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON SATELLITE
IMAGERY...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL
ANALYSIS.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1015 UTC.

TROPICAL WAVE E OF THE LESSER ANTILLES IS ASSOCIATED WITH THE
REMNANTS OF DORIAN AND EXTENDS FROM 22N57W TO 15N58W MOVING W 15-
20 KT. SCATTERED MODERATE/STRONG CONVECTION IS WITHIN 90/120 NM
OF LINE FROM 22N56W TO 18N61W.