Isaac lashing the Keys; an eyewall is building

By: Dr. Jeff Masters , 3:48 PM GMT on August 26, 2012

Share this Blog
44
+

Tropical Storm Isaac is steadily organizing as it lashes the Florida Keys with heavy rain and tropical storm-force winds. Sustained winds of 44 mph and 41 mph have been observed at Molasses Reef and Sombrero Key, respectively, this morning. Radar out of Key West shows an increase in spiral banding, and the beginnings of an eyewall. An Air Force Hurricane Hunter aircraft completed its first pass through the center of Isaac near 11:30 am EDT, and did not find the pressure had fallen, or that the peak winds had increased. Infrared and visible satellite loops show that Isaac is a large and increasingly well-organized storm. An analysis of upper level winds from the University of Wisconsin CIMSS shows that upper-level outflow is quite good and increasing to the north, but is lacking elsewhere. Moderate wind shear and dry air to the south are interfering with heavy thunderstorm development on Isaac's south side. Heavy rains from Isaac are lingering over Haiti and the Dominican Republic; flash floods in Haiti from Isaac's torrential rains killed at least four people.


Figure 1. Morning reflectivity image from the Radar out of Key West radar shows the northwest section of an eyewall beginning to form to the southeast of the city.

Latest model runs for Isaac
The latest set of 0Z and 06Z (8 pm and 2 am EDT) model runs have diverged significantly, and we can no longer be confident we know where Isaac will make landfall on the Gulf Coast. One camp of models, the UKMET and ECMWF, predict that a trough of low pressure moving across the Southeast U.S. will be strong enough to turn Isaac north to a landfall in the Florida Panhandle. The other set of models, the GFDL, GFS, and HWRF, predict the trough will bypass Isaac, and a ridge of high pressure will build in and force Isaac to a landfall over Louisiana. The official NHC forecast averages out these two extremes, calling for a landfall midway between the two solutions. Odds are, one of the two model solutions will turn out to be the correct one, and the NHC will be forced to make a substantial adjustment in their forecast track to the east or the west. Isaac has the potential to drop torrential rains capable of causing serious flooding and drought relief over the South. The latest 8-day precipitation forecast from the GFS model calls for 10 - 20 inches of rain over Southeast Louisiana, where it predicts Isaac will make landfall. The ECMWF model, however, these heavy rains will fall more over the Florida Panhandle, Alabama, and Georgia.


Figure 2. A hurricane forecaster's dilemma: which set of models is correct? The latest set of 0Z and 06Z (8 pm and 2 am EDT) model runs have diverged significantly. Our two top models--the GFS and ECMWF--have 72-hour forecasts that are about 350 miles apart. The ECMWF forecast is not shown here, but lies just to the west of the UKMET forecast (white line.)

Intensity forecast for Isaac
Isaac survived passage over Hispaniola and Cuba relatively intact. It's large size aided this. Isaac is over very warm waters of 31°C (88°F) with high total heat content in the Florida Straits, but is encountering moderate wind shear of 10 - 15 knots due to upper-level winds out of the southwest. This shear is predicted to relax to the light range tonight as an upper-level anticyclone becomes established over the storm. This should allow for more substantial intensification after Isaac passes the Florida Keys. However, the total heat content of the ocean decreases for Isaac Monday morning as it encounters a relatively cool ocean eddy in the Southeast Gulf of Mexico. If Isaac takes a more westerly track, passing due south of the Central Louisiana coast, the storm will encounter a modest warm eddy, which would aid intensification. The intensify forecasts from the various models are very divergent. The latest 06Z (2 am EDT) run of the GFDL model keeps Isaac as a strong tropical storm until landfall in Louisiana. Isaac will undergo rapid intensification into a Category 3 hurricane as it hits New Orleans, says the latest 06Z (2 am EDT) run of the HWRF model. The ECMWF model has Isaac as a strong Category 2 storm with a central pressure near 950 mb as it hits near the Alabama/Florida border.

Comparing Isaac with Ike of 2008
The current situation with Isaac is similar in some ways to that of Hurricane Ike of 2008. Ike spent considerable time over Cuba, weakening from a Category 4 to a Category 1 storm. The storm couldn't put its energy into building a strong inner core, but it was able to build up its outer rainbands that were over very warm waters. This resulted in a major expansion of its wind field, with tropical storm-force winds extending out 275 miles from the center at one point. Ike was able to intensify into a Category 2 storm on its path towards Texas, and had an unusually low pressure for a Cat 2 storm with 100 mph winds--944 mb. That's a central pressure more typical of a Category 3 storm, but Ike could only manage Category 2 winds, since it had such a large chunk of the atmosphere to keep spinning. With Isaac's TS winds already extending out to 205 miles, maybe we'll see another Ike-type situation as it intensifies--the storm will have an unusually low pressure in order to keep a huge wind field spinning, but never make it above Category 2, since it will take so long to spin up such a large wind field.

Storm surge forecast for Isaac
Isaac is a very large storm, with tropical storm-force winds that extend out 205 miles from the center. For comparison, Hurricane Katrina at landfall had tropical storm-force winds that extended out 230 miles from its center. Isaac's large size will enable it to set a large area of the ocean into motion, which will generate a large storm surge once the storm approaches land on the Gulf Coast. The latest 3:30 am EDT Integrated Kinetic Energy analysis from NOAA's Hurricane Research Division put the destructive potential of Isaac's winds near 0 on a scale of 1 to 6, but the destructive potential of Isaacs's storm surge was 2.1 on a scale of 1 to 6. A 2008 paper by Irish et al., The influence of storm size on hurricane surge, found that large storms like Isaac are capable to delivering a 30% larger storm surge to the coast than a smaller storm with the same maximum wind speeds. The angle with which the storm hit the coast is important, too--a storm moving due north or slightly east of north will deliver a storm surge about 10% greater than a storm moving NNW or NW. Consult our Storm Surge pages for detailed information on what the risk is for the coast. I expect that Isaac's storm surge will be about 30% higher than the typical surge one would expect based on the maximum wind speeds.

Invest 97L off the coast of Africa
A tropical wave (Invest 97L) is located about 650 miles west of the Cape Verde Islands off the coast of Africa. The storm has a modest amount of spin and heavy thunderstorms, and is under moderate wind shear. In their 8 am EDT Tropical Weather Outlook, NHC gave 97L a 50% chance of developing by Tuesday morning. None of the reliable models foresee that 97L will be a threat to the Lesser Antilles Islands. However, both the GFS and ECMWF models predict that a tropical wave that has not yet emerged from the coast of Africa may develop late this week, and potentially take a more westward track towards the Lesser Antilles, arriving around September 2.

Angela Fritz will have a new post here by 6 pm EDT. For the next few days, I plan to do the morning blog post, and Angela will be doing the late afternoon post. I'm in Atlanta to help out The Weather Channel with their on-air hurricane coverage, and will be on either in the afternoon or evening on Sunday, Monday, and Tuesday.

Jeff Masters

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 326 - 276

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45Blog Index

Quoting trHUrrIXC5MMX:
LATEST UPDATE ON ISAAC



new looking graphic

can you post that again
Member Since: Posts: Comments:
Watch it stay a TS until landfall....man, talk about overhyped, still looks ragged and all and it is flying....will be alot of sad sad bloggers if it does not turn into a major before it hits land....
Member Since: Posts: Comments:
Does anyone know where I can find current SSTs, SST Anomalies, and ocean current analysis for the Gulf? I will settle for just images, but I really would like to see some models. Everywhere I have checked has old data. Thanks!
Member Since: Posts: Comments:
Quoting weatherman12345:
Miami, r u still there? Did the CDO move into your area yet?
It appears so; a steady moderate rain with the occasional tropical storm-force gust. Nothing really unexpected yet, and the power is still going strong.
Member Since: Posts: Comments:
Quoting Lizardking1:
The focus is on NOLA of a direct hit, SOFL will be brushed by tropical storm winds and life moves on.

good point, but there still is minor street flooding
Member Since: Posts: Comments:
LATEST UPDATE ON ISAAC



new looking graphic
Member Since: Posts: Comments:
Another 50 knot flight winds:

162100 2410N 07919W 8447 01516 0054 +171 +154 158049 050 042 001 03
Member Since: Posts: Comments:
Quoting Tazmanian:




no the nhc made the right call by put a hurricane watch up for LA has its forcast too be come a hurricane later too day or tonight

well, i've got to agree with you too
Member Since: Posts: Comments:
The focus is on NOLA of a direct hit, SOFL will be brushed by tropical storm winds and life moves on.
Member Since: Posts: Comments:
Also remember the early track confidence because most of the models had a very similar early track.
Member Since: Posts: Comments:
Quoting GetReal:
Still needs to fill out some.
Member Since: August 14, 2010 Posts: 10 Comments: 16383
Quoting charlottefl:
Isaac is definitely moving more to the NW than it was earlier this morning. This may be temporary, but just interesting to note:
[...]
That perception may also be caused by tilt with height as he gets closer to the Key West radar.
Member Since: Posts: Comments:
Quoting capeflorida:
People here are just going to have to accept that Isaac was a dud for Miami and South Florida. If all of you would pay attention to what the storm had being doing and is doing, not what you thought it should be doing, you would have come to that conclusion a long time ago!
He has been a large TS in terms of size but nothing more than that!

While I am counting my blessings, the rain and howling wind we have been experiencing is anything but a "dud". This weather is exactly what I expected because I do lurk and learn here. Be careful in your generalizations. It is difficult to hear that what I am experiencing now is nothing because I just gotta tell ya it ain't.
Member Since: Posts: Comments:
Quoting 145:
Bottom line, NOAA shouldn't of made all kinds of warnings and watches for broward county if it is going to be a rain storm in a breezy day. Nhc should be more careful before warning everyone incorrectly and making them waste their money on supplies they won't need.

they say" possibility, not in actuality)
Member Since: Posts: Comments:
Quoting 145:
Bottom line, NOAA shouldn't of made all kinds of warnings and watches for broward county if it is going to be a rain storm in a breezy day. Nhc should be more careful before warning everyone incorrectly and making them waste their money on supplies they won't need.




no the nhc made the right call by put a hurricane watch up for LA has its forcast too be come a hurricane later too day or tonight
Member Since: Posts: Comments:
Quoting 145:
Bottom line, NOAA shouldn't of made all kinds of warnings and watches for broward county if it is going to be a rain storm in a breezy day. Nhc should be more careful before warning everyone incorrectly and making them waste their money on supplies they won't need.


lol, its not like you are going to use most of them anyway. This is the whole boy who cried wolf syndrome, the NHC made the right call, it is better to be safe then sorry. Unfortunately most do not feel that way, but maybe some day someone who feels that way will get more than they bargained for
Member Since: Posts: Comments:
Quoting Levi32:


After the last couple of days of attempting to forecast Isaac's track, I certainly am.
if he heads farther west, is there a better chance he gets to a warm eddy?
Member Since: Posts: Comments:
Very nice breeze ouside right now. It is till very muggy though.
Member Since: Posts: Comments:
Quoting WPBHurricane05:


Yet the Euro had Isaac going through the Yucatan Channel or south of Cuba. A long range win for the ECMWF, a medium range win for the GFS.
I posted this about 2 hours ago on the old blog.

GFS in the 3-5 day range, Euro in the 7-10.
Member Since: Posts: Comments:


14:47 GMT
Member Since: Posts: Comments:
Quoting washingtonian115:
I've seen more downcasting then hyping.




me two there been too marh downcasting this AM
Member Since: Posts: Comments:
Quoting angelafritz:


You make it sound like this storm has been forecast to get strong over and over and it never plays out. Which is not the case.

I think everyone in this blog needs to take a deep breath. Or two.

Actually, that's been exactly the case. Are you being sarcastic?
Member Since: Posts: Comments:
Quoting chrisdscane:
conditions r bad here in kendall

how bad
we got minor flooding and bent branches here so far
Member Since: Posts: Comments:
Quoting Tazmanian:



your acting like jfv

No he's not..
Taz why do you think everyone is JFV. ._.
Member Since: Posts: Comments:
Thanks for the analysis Dr. Masters. Really comes in handy since I think this storm is headed directly towards me now.
Member Since: September 20, 2005 Posts: 0 Comments: 369
Quoting shawn26:
I live in Cape Coral and I am keeping a very close eye on this.
In the Cape also and me too but calm :)
Member Since: Posts: Comments:
TWC said Key West area should experience 60 mph winds real soon.
Member Since: Posts: Comments:
Looking at GR3 there are a bunch of 50 knot winds in this band rolling into Key West.
Member Since: Posts: Comments:
Quoting SykKid:


starting to pull together. maybe you should sit back and realize that this storm is very slowly starting to get uts act together and that it's been forecasted to be stronger then it's ended up multiple times already.

that's true
Member Since: Posts: Comments:
conditions r bad here in kendall
Member Since: Posts: Comments:
293. dader
Quoting newportrinative:


This is what Broward should have done!

And Dade
Member Since: September 6, 2008 Posts: 0 Comments: 165
Quoting WxGeekVA:


Agreed. Everyone needs to calm down and stop hyping!

I've seen more downcasting then hyping.
Member Since: August 14, 2010 Posts: 10 Comments: 16383
Quoting shawn26:
I live in Cape Coral and I am keeping a very close eye on this.

good, on what side of the state though
Member Since: Posts: Comments:
Quoting southfla:
Basically, if you live in a hurricane risk area, it is a crap shoot every year. If you are within 20 miles of where the eye of the storm passes, your property might be at risk for a great deal of damage. If you are many miles away from the track of hurricane force winds when it makes landfall, your chances of serious damage are greatly reduced.

Some people are understandably nervous, upset or just annoyed at having their lives disrupted due to the storm. However, the hurricane does not care if you are inconvenienced. It does not care if you did or didn't prepare. What ever will happen will happen whether your are upset, nervous, angry or complacent. It pays to calmly prepare as best you can based upon the recommendations of your local officials and then hope for the best.

Statistically, most people under a hurricane warning (since the warning area is much larger than the width of hurricane force winds) will experience only minor damage and/or tropical force winds. Unfortunately, people who don't prepare take this to mean that their assessment of the situation was superior to the National Hurricane Center's and they will probably be less likely to prepare the next time.

It is a pain in the rear, but someday your gamble that nothing will happen when you are under a hurricane warning might not work out in your favor. I know several people in Homestead who were so sure Andrew was going to hit Miami, that they did not board up their homes. They lost everything. This is not to scare anyone.

Isaac, thank goodness, is not an Andrew and I don't think it will approach anywhere near that strength. So use common sense and realize that you are most likely preparing for nothing and BE GRATEFUL if that is how it turns out for you and your family. And the bonus is that you are much more ready if there is another threat this season.
good point
Member Since: Posts: Comments:
I live in Cape Coral and I am keeping a very close eye on this.
Member Since: Posts: Comments:
Quoting KRL:
Getting Isaac's intense outer squalls now in Palm Beach County. Heavy rain and strong winds. No lightning or thunder so far.

Local Weather Cam Link - Boca Raton Florida

same here
Member Since: Posts: Comments:
Basically, if you live in a hurricane risk area, it is a crap shoot every year. If you are within 20 miles of where the eye of the storm passes, your property might be at risk for a great deal of damage. If you are many miles away from the track of hurricane force winds when it makes landfall, your chances of serious damage are greatly reduced.

Some people are understandably nervous, upset or just annoyed at having their lives disrupted due to the storm. However, the hurricane does not care if you are inconvenienced. It does not care if you did or didn't prepare. What ever will happen will happen whether your are upset, nervous, angry or complacent. It pays to calmly prepare as best you can based upon the recommendations of your local officials and then hope for the best.

Statistically, most people under a hurricane warning (since the warning area is much larger than the width of hurricane force winds) will experience only minor damage and/or tropical force winds. Unfortunately, people who don't prepare take this to mean that their assessment of the situation was superior to the National Hurricane Center's and they will probably be less likely to prepare the next time.

It is a pain in the rear, but someday your gamble that nothing will happen when you are under a hurricane warning might not work out in your favor. I know several people in Homestead who were so sure Andrew was going to hit Miami, that they did not board up their homes. They lost everything. This is not to scare anyone.

Isaac, thank goodness, is not an Andrew and I don't think it will approach anywhere near that strength. So use common sense and realize that you are most likely preparing for nothing and BE GRATEFUL if that is how it turns out for you and your family. And the bonus is that you are much more ready if there is another threat this season.
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting samiam1234:
All this talk of Texas landfall is fairly ridiculous we are less then three days away from landfall. Typically NHChas very good track of less then 72 hours which is within the 100 mile region. I would guess this to go from new Orleans to Alabama or some where in the middle. Frankly I will be surprised if Galveston even sees a small sprinkle from this

the circulation is rather large
Member Since: Posts: Comments:
280. KRL
Getting Isaac's intense outer squalls now in Palm Beach County. Heavy rain and strong winds. No lightning or thunder so far.

Local Weather Cam Link - Boca Raton Florida
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting flcanes:

houston landfall?
o_o



your acting like jfv
Member Since: Posts: Comments:
Quoting angelafritz:


You make it sound like this storm has been forecast to get strong over and over and it never plays out. Which is not the case.

I think everyone in this blog needs to take a deep breath. Or two.
LOL Yes this blog is full of released, pent up energy. It's a bit infortunate, really. i posted a piture of my house under my photos if anyone wants to take a gander... if it's approved
Member Since: Posts: Comments:

Viewing: 326 - 276

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.