Tropical Storm Isaac, Part 2: Isaac Moving Into The Gulf Of Mexico-Hurricane Warnings For Morgan City, LA/MS/AL & FL Panhandle To Destin, FL

[wxmx]

BTW, the center "fix" we are talking about is around 14.5N

[andyhb]

To give us an idea...the 5 PM advisory had this at 16.0N...

[phil882]

BTW, the center "fix" we are talking about is around 14.5N

To give us an idea...the 5 PM advisory had this at 16.0N...

The surface winds were strong southwesterly though, implying the center is still highly decoupled.

[wxmeddler]

A bit late, but still worth while.. The 18z Sounding from San Juan.

[forkyfork]

the track into LA on the 18z gfs is because the model now builds a heat ridge to its north, much like the euro

[wxsniss]

I guess you meant southeasterly winds. The reason is that it's a very shallow vortex, 850mb and below, and recon is flying above that, where there is a strong easterly flow. If you look at the dropsonde you will see the SW winds there.

Center fix I was talked about from AF (not NOAA) flight, I believe located at 15.65N 66.4333W.

I was implying that the LLC is quite a bit displaced northeast of the upper level circulation.

As for low level winds, this buoy may be interesting to follow tonight, 15°3'14" N 67°28'19" W, also southwest of the last LLC fixes:

http://www.ndbc.noaa...p?station=42059

[CUmet]

NOAA P-3 plane confirms that the 700mb low is south of the weak LLC.

1002 mb extrapolated surface pressures for a long stretch.

Here is the twitter feed for the NOAA Jet.

HRD/AOML/NOAA ‏@HRD_AOML_NOAA

#NOAA42: At our Initial Point winds at flight-level very weak, surface winds strong, suggesting storm still disorganized

The LLC is anything but weak at this point...given dropsonde/SFMR readings of 40-45 kt surface winds on the north side, and the buoy obs of 30-35 kt SW winds on the south side.

The 700 mb center is still displaced from the surface-850 mb center, but note that the magnitude of displacement is no longer several hundred kilometers like it was yesterday. Yes, it's still not perfectly vertically stacked yet, but it's getting there.

[phil882]

The LLC is anything but weak at this point...given dropsonde/SFMR readings of 40-45 kt surface winds on the north side, and the buoy obs of 30-35 kt SW winds on the south side.

The 700 mb center is still displaced from the surface-850 mb center, but note that the magnitude of displacement is no longer several hundred kilometers like it was yesterday. Yes, it's still not perfectly vertically stacked yet, but it's getting there.

Finally got a good Windsat pass... looks like the center is around 16.5N 67W.

[andyhb]

Finally got a good Windsat pass... looks like the center is around 16.5N 67W.

So quite far north, then?

[Amped]

So quite far north, then?

It just confirms The NHC position was correct,it's not further south as some were saying.

[Ian]

..Isaac a little stronger as it continues moving

west-northwestward...

summary of 800 PM AST...0000 UTC...information

----------------------------------------------

location...16.2n 67.8w

about 190 mi...305 km SW of San Juan Puerto Rico

about 210 mi...340 km se of Santo Domingo Dominican Republic

maximum sustained winds...45 mph...75 km/h

present movement...WNW or 285 degrees at 16 mph...26 km/h

minimum central pressure...1002 mb...29.59 inches

watches and warnings

--------------------

changes with this advisory...

the government of the Dominican Republic has changed the Hurricane

Warning to a Tropical Storm Warning for the South Coast of the

Dominican Republic from Isla Saona westward to the Haiti-Dominican

Republic southern border.

Read more at

http://www.wundergro...fb5gvWDwKbew.99

[turtlehurricane]

Finally got a good Windsat pass... looks like the center is around 16.5N 67W.

Looks like some semblance of an inner core on that pass in the southern semicircle. Convection has gotten much deeper since the pass too. Will be interesting to see what the NOAA P-3 finds shortly, might finally get some legit pressure falls.

[wxmx]

Recon going for the kill...descended to 850mb

[CUmet]

Given how well-defined the low-level center was during the last pass at 1920z, it may very well just moved 0.9 degrees N and 1.5 degrees W over the past few hours instead of "relocating".

[wxmx]

It's clear there's a vortex at 16.5N, although many obs are missing, but it's quite small and mostly convection free....there's probably another one (low level also) to the S...we'll see what recon finds.

[turtlehurricane]

It's clear there's a vortex at 16.5N, although many obs are missing, but it's quite small and mostly convection free....there's probably another one (low level also) to the S...we'll see what recon finds.

Winds from the south where the plane is now, suggests the real center is off to the west of the plane's longitude by a good bit.

[LakeEffectKing]

It's clear there's a vortex at 16.5N, although many obs are missing, but it's quite small and mostly convection free....there's probably another one (low level also) to the S...we'll see what recon finds.

Good point....the next few MV images should interesting unter that ball.....

[wxmx]

Winds from the south where the plane is now, suggests the real center is off to the west of the plane's longitude by a good bit.

Yep...and pressure is lower also...so far 1001.2mb extrapolated, and probably a little less to the west as you mention.

[wxmx]

If there's confirmation of an LLC that far south...Hispaniola can do us a favor and get rid of the LLC to the north.

[turtlehurricane]

If there's confirmation of an LLC that far south...Hispaniola can do us a favor and get rid of the LLC to the north.

Just because they found the pressure trough at 15.4 °N doesn't mean the center is that far south, but it's possible. We need a real center intercept.

[wxmx]

Just because they found the pressure trough at 15.4 °N doesn't mean the center is that far south, but it's possible. We need a real center intercept.

Yes, I know. Hopefuly there's no comm problems, havent updated for almost 20 minutes now.

[wxsmwhrms]

Just because they found the pressure trough at 15.4 °N doesn't mean the center is that far south, but it's possible. We need a real center intercept.

Agreed. But the pressures are definitely lower farther S if the extrap values are accurate.

[wxsmwhrms]

I honestly think the Euro model is contaminated and an outlier..I just see Issac going north into South Florida,and across Fla,westward shift westward shift, holly crap,the dam thing isn't even in the EGOM yet...How Euro hungry can one be..what the hell I am just a dam weather weenie from Maine what do I know.

Uh, "contaminated" by what, number one?

Number two, it's not just the Euro. The GFS, UK and EC (and their ensembles) are now all showing landfall somewhere from LA to near Mobile.

Number three, from a synoptic and climatological perspective, a landfall over the central Gulf coast makes a lot of sense. This system is being primarily guided by strong ridging without any significant trough. The models agree on a dominant ridge setting up east of FL during the day 3-6 period. That strongly suggests a WNW track toward somewhere on the northern Gulf Coast.

[Connor McCrorey]

Yes, I know. Hopefuly there's no comm problems, havent updated for almost 20 minutes now.

There we go, looks like they're heading NE away from the center.

Those SSE winds at their current location really make me think Isaac has a slowly deepening LLC to the south. Hopefully they head straight in on this pass.

[wxsouth]

Agreed. But the pressures are definitely lower farther S if the extrap values are accurate.

Problem is, all of the 1001-1002mb extraps came after they ascended back to 700mb, so the pressure estimates are likely too low.

[turtlehurricane]

Problem is, all of the 1001-1002mb extraps came after they ascended back to 700mb, so the pressure estimates are likely too low.

I wouldn't trust it either, oftentimes the pressure calibration is different between NOAA planes and airforce, dropsonde is the only way to be sure. Maybe they did drop one and it'll show up soon.

San Juan radar detecting a circulation at an altitude of 4.9 km centered in an area of convection at 16.7 °N, 67.9 °W.

[wxsmwhrms]

Just a note that the GFS ensemble looks well clustered along the 18Z ops run. There are now no longer any members east of about the far eastern GOM - but there are also no members as far west as the op EC with it looking like the farthest west member being about SE LA.

EDIT: FWIW (and I know it's not much) HWRF has shifted from being east of the track to west. Has landfall as a minimal hurricane (literally 64 kt) over right over the bird's foot of SE LA at 120 hours. These GFS based models seem pretty fast which is why (at least partially) I am guessing they don't intensify the system quite as much as the EC would imply as they have quite a bit less time over the Gulf.

[SN_Lover]

As of right now anticyclonic flow is still visible at the NE quadrant of the tropical storm, inhibiting growth. Shear is VERY low and the SST's are crazy. So when the dry air gets out of the storm and anticyclonic flow stops, then this will rapidly intensify. Nothing is preventing this system from going into the gulf, except the trough in the southeast which will move the system NE upon landfall. The Euro has been catching on to a weaker system and the high pressure situated in the Atlantic not weakening.

This does have relevant information in it so please don't delete

[turtlehurricane]

Some shots of the apparent circulation at roughly 16.8 °N, 67.9 °W. I checked the other tilts and it's persistent for a long ways up. Really curious as to whether this is simply one of several mesovortices or the true center. The way radar echoes seem to be orbiting the point for hundreds of miles makes me think it's the real deal though...

[wxsmwhrms]

Problem is, all of the 1001-1002mb extraps came after they ascended back to 700mb, so the pressure estimates are likely too low.

Excellent points from you and turtle. I didn't realize they weren't at the same altitude.