Ida weakens to a tropical storm; tropical disturbance 96E kills 124 in El Salvador

By: Dr. Jeff Masters , 3:20 PM GMT on November 09, 2009

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Tropical Storm Ida is steadily weakening as it hurtles northwards towards the Gulf of Mexico coast. Rains from Ida have already pushed into south-central Louisiana, where radar estimates indicate up to an inch of rain has fallen. Winds along the Gulf Coast of Mississippi, Alabama, and the Florida Panhandle were 20 - 25 mph this morning, and will steadily increase today as Ida draws near. Winds at the Mississippi Canyon buoy 150 miles south of Gulfport, MS were sustained at 45 mph at 8 am EST this morning, with 19 foot waves.


Figure 1. Microwave "radar in space" image of Ida taken at 7:15 am EST on Monday, 11/9/09. The eye is visible as a dark spot, but the eyewall has partially collapsed. The strongest echoes are on the north side of the storm, and Ida's heaviest rains and highest winds will hit the coast tonight, well in advance of the arrival of the center. Image credit: Navy Research Lab, Monterey.

Infrared and visible satellite loops show that wind shear has substantially degraded the appearance of Ida, and there is very little heavy thunderstorm activity in the storm's eyewall. Most of Ida's heavy thunderstorms have been displaced to the north of the storm, due to strong upper-level winds out of the southwest creating 30 knots of wind shear. Water vapor satellite imagery reveals a large area of dry air to the southwest of Ida, and the shear has now driven this dry air deep into the core of the storm, significantly disrupting it. The latest 6:30am EST vortex report from the Hurricane Hunters reported that the eyewall was ragged, and the pressure had risen to 997 mb. A recent microwave satellite image of Ida (Figure 1) shows that the eyewall is weak and has partially collapsed. Ida's most intense thunderstorms are on the north side of the storm, and the heaviest rains and highest winds will hit the coast tonight, well in advance of the arrival of the center.

The intensity forecast for Ida
The intensity forecast models predict that Ida's winds will range between 50 - 65 knots (58 - 74 mph) at landfall. The high wind shear of 30 knots currently affecting Ida is forecast to increase to 40 knots by late afternoon, and 55 knots by midnight. With Ida now over waters near 26°C, which is barely enough to support a hurricane, and with water temperatures decreasing to 23°C near the coast, the combination of high wind shear and cold waters will act to significantly weaken Ida. However, Ida is beginning to transition to an extratropical storm, and it is often the case that during such a transition the winds will gain energy from the process, though that's looking unlikely in this case. I expect Ida's top winds will be in the 50 - 60 mph range along the coast tonight and Tuesday morning. Regardless of Ida's strength at landfall, the storm will be able to dump 4 - 8 inches of rain along the Gulf Coast and well inland. We can't rule out the possibility of an isolated tornado when Ida makes landfall, but the Storm Prediction Center Discussion maintains that the airmass in place over the Gulf Coast is relatively stable, and prospects for an appreciable severe weather threat appear low.


Figure 2. Maximum storm surge (depth of water above ground) for a Category 1 hurricane with 85 mph winds moving north-northeast at 15 mph. Ida is expected to be moving at this speed and direction at landfall, but will be much weaker, so surges will not be this high. Furthermore, the storm will not create this level of surge along the entire coast--the image above is a composite worst-case scenario for all the storms shown by the black tracks with arrows. Image credit: NOAA SLOSH model run for Mobile Bay, 2008 version. Heights are given relative to the NAVD88 datum.

The storm surge forecast for Ida
Storm surge is the other major concern for Ida. With a strong high pressure system anchored over the U.S. today, the pressure difference between this high and Ida is creating a strong pressure gradient that was driving tides 2.5 feet above normal at Shell Beach, LA (on the east side of New Orleans) this morning, one foot above normal at Dauphin Island, AL, and one foot at Pensacola, FL (Figure 3). NHC is now calling for a storm surge of 3 - 5 feet above ground level, which is a reasonable forecast even if Ida weakens further. A large stretch of coast will be subject to very high water levels for an extended period of time today and tomorrow, with battering waves on top of the surge likely to cause a significant coastal erosion event. A particular concern is the western end of Alabama's Dauphin Island, when even a strong tropical storm can cause significant damage to the low-lying, heavily developed barrier island. The tidal range along the Gulf Coast varies by about 1.5 feet between low and high tide, and high tide is near 2 am EST on Tuesday.




Figure 3. Observed vs. predicted water levels at three coastal stations. Top: Shell Beach, LA (just east of New Orleans); middle: Dauphin Island, Alabama; bottom: Pensacola, FL. The green line shows how high above normal the water is. For Shell Beach, it was 2.5 feet above normal at 9am CST, while it was just over 1.0 feet above normal at the other two locations. Image credit: NOAA Tides and Currents.

Comparing to Hurricane Kate
The last November hurricane in the Gulf of Mexico was Hurricane Kate. Kate struck the Florida Panhandle near Mexico Beach on November 21, 1985 as a Category 2 storm with 105 mph winds. According to Wikipedia, Kate killed five people in Florida and did $300 million (1985 dollars) in damage. Ida will cause relatively minor damage compared to Kate.

Links to follow:
U.S. Severe Weather Page
Wundermap for the Gulf Coast of Alabama.
Long-range radar out of New Orleans, LA.
Navarre Beach, FL webcam.
Coastal observations from the University of South Alabama.
Coastal observations from LSU.

El Salvador floods kill 124
Heavy rains that began on Thursday due to tropical disturbance 96E have killed at least 124 people in El Salvador, with 60 people still missing. The flooding hit the capital of San Salvador and rural areas to the east. The heavy rains were due to tropical disturbance 96E (Figure 4), which formed off the coast of El Salvador on Wednesday, November 4. The counter-clockwise flow of air around the disturbance pulled large quantities of moist, Pacific air over the coastal mountains in El Salvador, dumping heavy rains of up to five inches, according to satellite estimates. The rains must have been much heavier over a small area that the satellite could not resolve. The terrible devastation I'm seeing in news photos indicates much higher rains of perhaps 10 - 15 inches must have fallen in a concentrated area in the mountains.


Figure 4. Satellite image of tropical disturbance 96E, which moved over El Salvador Thursday through Saturday, bringing heavy rains. Also pictured is Tropical Depression Eleven, which intensified into Tropical Storm Ida later that day. Ida was not responsible for the flooding in El Salvador, though it may have helped pull 96E into El Salvador. NASA has a nice zoom image> of 96E from November 5.

I'll have an update on Ida this afternoon.

Jeff Masters

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Question: Some models bring the remnant low back south along the Florida coast. But wouldn't the moisture field keep going north? The models are a little confusing. Come on someone can answer this.
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Quoting StormW:
atmoaggie,
What up?

Virga. Howdy, StormW.

Hope these folks are aware, but few will prolly perish from this one regardless.



Can you imagine for a moment if this were to make landfall as a cat 2? 3 days, or less, after leaving Honduras?
With most folks not paying any attention at all to the tropics?
Could have been a lot uglier than it is going to be, thankfully.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Much ado about nothing, imagine that.
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If I remember correctly, the Perfect Storm had a small warm core area around a nontropical area.. similar situation here.. small deep convection around large swells of convection.
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AOI

AOI

AOI

AOI

TS BUSTED FORECAST, to be used in the event you make a minor discrepancy in your forecast.
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Quoting atmoaggie:

Oh, that? That is Fred-Ex. Back from his second round-the-world tour.


I needed a good laugh!!
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Good work, Storm! The Met coulda just left it at this:

...INSTEAD A FUNCTION OF THE INTENSE LATENT HEATING FROM SIMULATED DEEP CONVECTION (CONVECTIVE FEEDBACK).
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Woah. That is some re-firing. A lot of convection and cold cloud-tops building in the last hour, though rather small:


Loop is best view: http://www.ssd.noaa.gov/goes/flt/t2/flash-jsl.html
Member Since: August 16, 2007 Posts: 6 Comments: 12463
She's a fighter. Perhaps her last name is Ingram... Convection flaring up again.
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What are rain estimates through Wednesday?
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Quoting gordydunnot:
Looking at visible there something I dont like about this storm.If its not getting a second wind this morning looks are deceiving.The combining systems look to be organizing better, anybody who knows what there talking about want to rip me no problem.
She's trying to regain her sea legs after getting blown down last night
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Quoting 850Realtor:
Dumb question, don't laugh...can a pressure drop outside make you dizzy? Not real bad, just feel kind of off?
Conditions feeling tropical around here. Stiff breeze, rain just starting.


Sure it can. Not drastic, but certainly could cause the slight 'off' feeling you described. If the pressure is falling faster than the air cavities in the sinuses can equalize due to some upper respiratory inflammation or congestion, you could feel it.

If it becomes bothersome, grab a piece of gum and chew it. The motion of the jaw will likely allow the pressures to equalize more easily.
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Quoting gordydunnot:
Looking at visible there something I dont like about this storm.If its not getting a second wind this morning looks are deceiving.The combining systems look to be organizing better, anybody who knows what there talking about want to rip me no problem.


*agreed*

I don't know what the heck I'm talking about, but both the visable and infrared make Ida look like she's getting more organized.
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Quoting atmoaggie:


Well, that might mean that the TS-force windfield isn't expanding by leaps and bounds, something we expected to happen.

Or, the NHC has reason to discount that H*Wind analysis...

Cannot get the NHC swaths to show, trying again:

This may shrink a bit if they have confidence in the H*Wind analysis product.

And the obs embedded in the analysis:

(with the lightest blue being the previous analysis used as a background, the rest are obs)


Got it, I thought you meant it may be trying to ramp up one last time.
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Quoting Grothar:


I know the conversation is on Ida, but just wonderded if anyone had noticed the blob NE of the Island? Probably just the normal November flare-ups. Go ahead, I am ready for the blasts. Be kind!

Oh, that? That is Fred-Ex. Back from his second round-the-world tour.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting ElConando:


Its remnants of every sheared tropical system we've had, they are out for revenge!


It has been a strange season!
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Looking at visible there something I dont like about this storm.If its not getting a second wind this morning looks are deceiving.The combining systems look to be organizing better, anybody who knows what there talking about want to rip me no problem.
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Maybe Reedzone, we can call it an "Imperfect Storm" !
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seems like the interaction with the low to its west is helping increase convection associated with ida
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Quoting ElConando:


To an idiot like me what does this mean?


Well, that might mean that the TS-force windfield isn't expanding by leaps and bounds, something we expected to happen.

Or, the NHC has reason to discount that H*Wind analysis...

Cannot get the NHC swaths to show, trying again:

This may shrink a bit if they have confidence in the H*Wind analysis product.

And the obs embedded in the analysis:

(with the lightest blue being the previous analysis used as a background, the rest are obs)
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting Grothar:


I know the conversation is on Ida, but just wonderded if anyone had noticed the blob NE of the Island? Probably just the normal November flare-ups. Go ahead, I am ready for the blasts. Be kind!


Its remnants of every sheared tropical system we've had, they are out for revenge!
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Can you answer post 50 plz?
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Maybe it's from staring at this netbook screen for 3 days or however long we've been watching this now :)
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Quoting 850Realtor:
Dumb question, don't laugh...can a pressure drop outside make you dizzy? Not real bad, just feel kind of off?
Conditions feeling tropical around here. Stiff breeze, rain just starting.



Yeah but it would have to be quite a pressure drop.
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Quoting 850Realtor:
Dumb question, don't laugh...can a pressure drop outside make you dizzy? Not real bad, just feel kind of off?
Conditions feeling tropical around here. Stiff breeze, rain just starting.

It can cause migraines so I don't see why it can't cause a little vertigo or dizziness.
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Dumb question, don't laugh...can a pressure drop outside make you dizzy? Not real bad, just feel kind of off?
Conditions feeling tropical around here. Stiff breeze, rain just starting.
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Quoting atmoaggie:
Thanks Dr. M.

"Rains from Ida have already pushed into south-central Louisiana, where radar estimates indicate up to an inch of rain has fallen"

I wonder if that includes the 24 hours of Virga? Surely something has hit the ground by now, though.


At least here in Ascension Parish, very little has hit the ground so far - just some light misting at times.

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Quoting atmoaggie:
Ida's 35 knot contour has actually been reigned inward a bit since earlier this morning.

H*Wind analysis from surface/HH/satellite obs:



In direction opposition to the last update to this:


To an idiot like me what does this mean?
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Quoting divdog:
looks to me that ida is tring to suck in moisture from the othe low to its west. i'm an amateur so this is just my thoughts.


Thats it.
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Quoting Grothar:


I know the conversation is on Ida, but just wonderded if anyone had noticed the blob NE of the Island? Probably just the normal November flare-ups. Go ahead, I am ready for the blasts. Be kind!


WTH is that?
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Storm: Nice analysis.
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Quoting FSUCOOPman:
What's going on around the COC that resembles strengthening in the last few visable frames: Link
looks to me that ida is tring to suck in moisture from the othe low to its west. i'm an amateur so this is just my thoughts.
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Ida's 35 knot contour has actually been reigned inward a bit since earlier this morning.

H*Wind analysis from surface/HH/satellite obs:



In direction opposition to the last update to this:
Member Since: August 16, 2007 Posts: 6 Comments: 12463
So what is causing the new convection ? A warm eddy maybe ?, lessening shear ? or what ?
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Quoting ElConando:


Remnants of a tropical system would be more of that wording I would use but yes.


Yeah, re-edited that post, Tropical Storm force winds, cause an Nontropical Storm can have high winds, with heavy rains.. It just looks like it's getting absorbed into one big mess, can't necessarily call it a "Perfect Storm"..
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Quoting reedzone:


I sure do see that! Still a dangerous situation in the Gulf, Tropical Storm hanging around for days is not the best of news.


Remnants of a tropical system would be more of that wording I would use but yes.
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I know the conversation is on Ida, but just wonderded if anyone had noticed the blob NE of the Island? Probably just the normal November flare-ups. Go ahead, I am ready for the blasts. Be kind!
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What's going on around the COC that resembles strengthening in the last few visable frames: Link
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Quoting ElConando:
If you look at visible it looks like the convection of the west of Ida is starting to get sucked in.


I sure do see that! Still a dangerous situation in the Gulf, Tropical Storm force winds hanging around for days with constant flooding is not the best of news.
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for anybody in my area. they just closed okaloosa county schools for tuesday.
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If you look at visible it looks like the convection of the west of Ida is starting to get sucked in.
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Thanks for the update Dr. Masters. Yesterday they were saying the deaths in El Salvador were caused by IDA, but I96 made more since.
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Mornin all. Guess things have simmered down some. Still. Getting rain here in Comanche, TX. Must be covering quite a bit of real estate.
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Quoting LaCoast:
What happened to the Perfect Storm and a Tampa landfall, and a south movement etc etc. It has been postponed to a date and time not yet determined!
Member Since: August 25, 2008 Posts: 0 Comments: 633
Quoting atmoaggie:
I don't think I would call that a re-firing. But there is a little more convection that hasn't been displaced to the NE...yet.


(We were seeing large swaths of the light red and sprinkles of the green yesterday at this time. That prolly looks funny when it hits the ground...red rain mixed with a little green rain...)


lol didn't see the bottom quote. That would be quite an experience. I have heard to colored rain before though. It is very rare though.
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Orcasystems -- Thanks for the links! :)

Does anyone know of the correlation btwn seismic activity and tropical weather/storms on the opposite side of the Earth? I remember hearing something on the Discovery Science channel once and then reading something in someone's blog on here saying basically the same thing. But I cannot remember the explanation of why or how? Anyone else every heard of this?
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It's a shame that the price of oil is rising, and now, according to news reports, they are using "threat of Ida" as an excuse. Just last week, before Ida, the reason was the value of a dollar. Additionally, there was plenty of oil for use, actually too much.
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Ida GHCC loop GOES in rapid scan, so additional images.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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