ATL: ISAAC - Post-Tropical - Discussion

[KWT]

Sure does Frank, I'm not surprised as the system looks on the Vis.imagery to be wrapping around the center.

Its going to be interesting to see what recon finds this time round when it reaches it.

[RL3AO]

Question for anyone....do the 12z models get incorporated into the 11:00 AM advisories? I know I can't see them until 11:30 AM, but when does the NHC get the data?

The late cycle models (basically the GFS and ECMWF as well as the consensus models) aren't available until after advisory time. Its why they're called late cycle. For the 15z advisory, they would use the 6z GFS interpolated six hours and 0z Euro interpolated 12 hrs.

[hurricanes1234]

Isaac reminds me very much of Ernesto. Here's why:

1. Isaac is almost in the same place as Ernesto.
2. It is almost the same size as Ernesto when he was here, except, most likely Ernesto was smaller.
3. Most importantly, Isaac is suffering from a similar problem that Ernesto was suffering from - dry air intrusion. The NHC mentioned in a couple of Ernesto's discussions that conditions were favorable for rapid intensification but it just needed to mix out the dry air. A similar thing was mentioned in Isaac's discussion at 11 AM. Ernesto also had the same problem in which its circulation was poorly defined.

I think Ernesto and Isaac are brothers.

[Zeno8]

Interesting. JB is sticking to his guns. Admits he could be wrong, but still sticking to a east Fl landfall. Then north along the coast.

Let hope not. We are saturated here in North Fl with another inch or two on the way today. The NHC has been amazing so I have stuck with them since Katrina. IT WOULD BE NICE TO NUDGE THIS TO THE WEST AND PLOW THIS THING INTO THE CENTRAL PLAINS WHERE THEY NEED THE RAIN.

AMEN let's get some productivity out of it!

[GTStorm]

Question for anyone....do the 12z models get incorporated into the 11:00 AM advisories? I know I can't see them until 11:30 AM, but when does the NHC get the data?

No. Models take a while to run, a lot of data. The 12Z models started at 8AM EDT, we only start getting the output around 11:30AM.

Someone please correct me if I'm wrong.

OK thanks, so 12z is the start time of the model, not when it is finished spitting out the data?
And to me that is interesting, the NHC comes out with a forecast track update and then 30 minutes later has access to brand new model data.

[KBBOCA]

There are pictures of some pretty bad flooding in Trinidad & Tobago at Storm Carib:
http://stormcarib.com/reports/current/trinidad.shtml

Just goes to show you that it's not always where the center hits. Guadeloupe, Dominica and Martinique which seemed to be in Isaac's "bullseye" seem to have gotten off quite lightly, while some of the southern islands got hit with extreme rains and flooding from the heavy southern feeder bands.

A very good lesson and reminder that a storm is not a "point" or a line, and that the exact track and cone is not always what matters in assessing impact. Storm size and the precipitation distribution in the various quadrants of the storm are really important too.

I believe i'm correct that Trinidad & Tobago were not even under TS watches for Isaac since they are so far south of the center...!

[wxwatcher1999]

Sure does Frank, I'm not surprised as the system looks on the Vis.imagery to be wrapping around the center.

Its going to be interesting to see what recon finds this time round when it reaches it.

Last I saw they found multiple vortices and only 35 kt winds...not organizing yet in my opinion

[TeamPlayersBlue]

The dry air is still doing a number on this storm and i think its a good thing. Once the dry air is gone it could blow up into a monster. From the look of the cone, if its going to head on its predicted path it should start turning soon here.

[Tyler Penland]

Interesting. JB is sticking to his guns. Admits he could be wrong, but still sticking to a east Fl landfall. Then north along the coast.

Let hope not. We are saturated here in North Fl with another inch or two on the way today. The NHC has been amazing so I have stuck with them since Katrina. IT WOULD BE NICE TO NUDGE THIS TO THE WEST AND PLOW THIS THING INTO THE CENTRAL PLAINS WHERE THEY NEED THE RAIN.

At what cost? If this thing were to get its act together and track all the way across the GOM towards TX/Central Plains, first off we'd be paying more for gas than ever before, and secondly, well, just look at what the Euro has been showing as far as intensity.

[KWT]

LOCATION...15.6N 65.4W

Looking at the radar and the sat.imagery, I think this maybe moving closer to NW than I first thought, maybe 300-305.

Models have done a pretty good job thus far with this systems track.

[RL3AO]

Question for anyone....do the 12z models get incorporated into the 11:00 AM advisories? I know I can't see them until 11:30 AM, but when does the NHC get the data?

No. Models take a while to run, a lot of data. The 12Z models started at 8AM EDT, we only start getting the output around 11:30AM.

Someone please correct me if I'm wrong.

OK thanks, so 12z is the start time of the model, not when it is finished spitting out the data?
And to me that is interesting, the NHC comes out with a forecast track update and then 30 minutes later has access to brand new model data.

If you start reading near the bottom of page 7 of this document it explains the early and late cycle models.

http://www.nhc.noaa.gov/verification/pd ... n_2011.pdf

[Aric Dunn]

LOCATION...15.6N 65.4W

Looking at the radar and the sat.imagery, I think this maybe moving closer to NW than I first thought, maybe 300-305.

Models have done a pretty good job thus far with this systems track.

all you have to do is look at the last few recon fixes before they and you will see the motion.

[wxman57]

I still think Isaac's center (most of them) will miss Haiti and graze that east-west part of the eastern Cuba coast passing just east of Havana on Sunday. Maybe about 40-70 miles west of the NHC track for days 1-3. Their 5-day point and track heading west of Apalachicola looks ok. Looking more like the Florida Peninsula won't receive any hurricane conditions. Pensacola to Apalachicola (maybe near Panama City) is where I think it'll make final landfall. Of course, if you're located in south Florida you should be preparing for the worst - just in case. But I'd be breathing a sigh of relief if I lived on the Peninsula - just as I did when the track of then Cat 5 Rita shifted from west of Galveston Bay to east of Galveston Bay that Thursday morning, Sept. 11th.

[wxwatcher1999]

LOCATION...15.6N 65.4W

Looking at the radar and the sat.imagery, I think this maybe moving closer to NW than I first thought, maybe 300-305.

Models have done a pretty good job thus far with this systems track.

Canyou post the radar you are looking at and with it still having multiple vorticies could that just be an illusion?

[cycloneye]

This is Dr Jeff Masters discussion of Issac and possible impacts down the road with the 11 AM Advisory information.

Posted by: Dr. Jeff Masters, 11:13 AM AST on August 23, 2012

Tropical Storm Isaac is a large and impressive-looking storm on satellite images, but data from the Hurricane Hunters reveal that Isaac remains a minimal-strength tropical storm with 40 mph winds, as it heads westward across the Eastern Caribbean. An Air Force Reserve hurricane hunter aircraft which completed its mission into Isaac at 8 am EDT found top winds at the surface near 40 mph, and highest winds at their 5,000 foot flight level of 47 mph. A NOAA hurricane hunter aircraft flying at 10,000 feet has found top winds of 47 mph at that altitude. The Hurricane Hunters found a broad area of light winds with a central pressure of 1003 mb. The aircraft did not observe an eyewall trying to form, and recent microwave satellite images also show no signs of an eyewall forming. There does not appear to be much in the way of dry air near the core of Isaac, as seen on water vapor satellite loops, which is a big switch from what we've seen previously. Visible satellite loops show that Isaac has a much more symmetric circular cloud pattern, and has developed a Central Dense Overcast (CDO) of high cirrus clouds, the hallmark of an intensifying storm. These clouds have very cold cloud tops, indicating that the updrafts creating them are quite strong. An analysis of upper level winds from the University of Wisconsin CIMSS shows that an upper-level pattern of outflow supportive of significant strengthening has developed this morning, with an upper-level outflow channel now well-established to the north, and a new outflow channel opening to the south. Radar imagery from Puerto Rico shows some weak low-level spiral bands that are slowing intensifying and becoming more organized.

Intensity forecast for Isaac

Isaac has consistently confounded predictions that it would intensify, but all the potential factors inhibiting intensification seem to have diminished to the point where intensification has to occur. Wind shear is low, 5 - 10 knots, and ocean temperatures are warm, 29°C, and these warm waters extend to great depth, giving the storm a high total heat content to work with. These factors, combined with the favorable upper-level outflow pattern and more symmetric cloud pattern, support intensification, and all of the intensity models except the HWRF model predict intensification of Isaac to a strong tropical storm or Category 1 hurricane by Friday afternoon. The latest 8 am EDT run of the SHIPS model predicts that wind shear will be light to moderate, 5 - 15 knots, for the next five days. The 11 am EDT wind probability forecast from NHC predicted a 34% chance that Isaac will become a hurricane by Friday afternoon, and a 6% chance it will be a Category 2 or stronger hurricane then. By Friday afternoon, Isaac will likely be close enough to Southwest Haiti that the inner core will be disrupted, and the storm will likely be a 45 - 55 mph tropical storm on Saturday and Sunday as it moves over Cuba. Once Isaac pops off the coast of Cuba into the Florida Straits, it will be over very warm waters of 31 - 32°C (88 - 90°F), wind shear will be light to moderate, and the upper-level wind pattern favorable for intensification, with low wind shear due to an upper-level anticyclone over the storm. It will probably take at least 24 hours with the storm's center over water for it to become a hurricane.

Impact of Isaac on the Islands

The south coast of Puerto Rico should see Isaac's heaviest rains and strongest winds beginning near 8 pm EDT tonight, with tropical storm-force winds of 40 - 45 mph potentially affecting the southwest portion of the island. The San Juan airport may be able to stay open during Isaac's passage, but with delays when spiral bands move overhead.

Heavy rains and tropical storm-force winds should arrive on the southern coast of the Dominican Republic late tonight, and the Santo Domingo airport will probably be closed on Friday. Rainfall amounts of 8 - 12 inches will likely affect the Dominican Republic Thursday through Saturday, creating dangerous flash floods and mudslides.

Isaac is potentially a very dangerous storm for Haiti, where 400,000 people still live outside underneath tarps in the wake of the 2010 earthquake. Heavy rains from Isaac will begin on Friday morning in Haiti, and last through Sunday. Rainfall amounts of 8 - 12 inches are possible, which will be capable of causing extreme flooding on the vegetation-denuded slopes of Haiti. It will be a major challenge to keep those Haitians living outside safe, if rainfall amounts of 5 - 10 inches occur.

Impact on Florida, Cuba, Jamaica, and the Bahamas

Florida, Cuba, Jamaica, and the Bahamas are all at risk of receiving flooding rains and high winds from Isaac. The latest set of 00Z (8 pm EDT) and 06Z (2 am EDT) model runs for Isaac are fairly unified for the coming three days, showing a west-northwestward track over Southwest Haiti and into Western Cuba. At the 4 - 5 day forecast period for Sunday and Monday, the models have come into better agreement, and have shifted west some. Our best-performing model, the ECMWF, has now shifted Isaac's path more to the east, but still is the westernmost of the models, predicting a landfall for Isaac near the Alabama/Florida border on Wednesday. While we do still have some models predicting a path up the east coast of Florida, model consensus now favors a path up the west coast of Florida through the Gulf of Mexico. The recent reformation of Isaac's center more to the south supports the idea that Isaac will take a track more to the west through the Gulf of Mexico. Since this now means a final landfall for Isaac in the Florida Panhandle is likely, the storm will probably have an extra day over water, increasing the odds that it will become a Category 2 or stronger hurricane before this final landfall. The NOAA jet is scheduled to fly into the storm this afternoon, to do a large-scale dropsonde mission to aid model forecasts. These missions can improve model forecasts by 10 - 20%, so the model runs that will be available early Friday morning should have increased reliability.

[alienstorm]

Seems now to be getting its act together. Should be interesting afternoon.

[WeatherGuesser]

IT WOULD BE NICE TO NUDGE THIS TO THE WEST AND PLOW THIS THING INTO THE CENTRAL PLAINS WHERE THEY NEED THE RAIN.

Roger That. As long as we would only get the rains and not the damaging winds.

But I'm afraid CONTROL's Cone Of Dryness would still win out somehow like it has all summer.

On another note, I'm seeing conflicting stories that they are considering cancelling or postponing the convention. Other stories say they've already decided to go ahead as planned.

[KWT]

LOCATION...15.6N 65.4W

Looking at the radar and the sat.imagery, I think this maybe moving closer to NW than I first thought, maybe 300-305.

Models have done a pretty good job thus far with this systems track.

all you have to do is look at the last few recon fixes before they and you will see the motion.

I don't know whether you were awake, but the first few fixes were on a different center, it was only 2/3rds of the way through the flight that they found the more defined center (you can tell by the way the wind shift is large and uniform) from then on recon focused on this northern area.

So in truth, that motion wasn't likely actually real, more like they missed the main center for a secondary vortex, then found the stronger center a little later on.

[Aric Dunn]

well the last two for sure were the better defined center from the airforce plane the noaa plane also continued that center. so there is plenty of fixes to use

[cycloneye]

Latest microwave.