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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I am very suprised that they dropped the hurrcane advisories so abruptly well over 12 hours out from the forecasted landfall.
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Looks like Ida could make land fall way before 6am. Is there anything that could slow her down
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Quoting StormSurgeon:
Ida is gonna finish wrapping up and hit Mobile. Dauphin Island landfall. Rainy and gusty tonight for us.
I wouldnt be suprised if she goes a little West of us.
Quoting IKE:


Yeah...I'm here. Went to Wal-Mart to get dinner and some chicken tenders.

Hmmm...their good.


Love their hot wings, may get some in a few minutes.
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HH home air port in Biloxi.
"It's headed for Biloxi!" I remember that line from Ivan...
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NEXRAD Radar
New Orleans, Storm Relative Mean Radial Velocity 1.45 Degree Elevation Range 124 NMI

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Ida is gonna finish wrapping up and hit Mobile. Dauphin Island landfall. Rainy and gusty tonight for us.
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Quoting atmoaggie:
70 knots surrounded by flagged data...withholding opinion for the moment.

http://tropicalatlantic.com/recon/URNT15/KNHC/


My thinking also, manual QC may reject those.
Member Since: September 23, 2005 Posts: 14 Comments: 10883

Reply to taco...westend of dauphin island has some overwash. No surprises there !!! Police have roadblocked when I was on that end about tenish. About st stephens street. Water bareley went down by inches with dropping tide. Should be something to watch on incoming! Bay is very rough already.
Somethin lurkin just off shore, that's for sure !



You all are killin me, no lunch yet. Gotta go get some now, chicken nugget taco's, yum :)
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Looks like its going to be Mobile on the E side.
515. IKE
Quoting Halyn:
I just got here .. has anyone heard from Oz and/or Ike ??


Yeah...I'm here. Went to Wal-Mart to get dinner and some chicken tenders.

Hmmm...their good.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting ElConando:


Okay is orange TS winds?

Yes.
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Quoting Patrap:
IDa on NOLA Medium Range Radar



Will we get rain you think Pat?
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Quoting Jedkins01:



The one issue with the water vapor sattelite image, is it only gives you an example of the upper atmospheric situation.

For Example, many times we have had 2.00 + PWAT air where there is deep layer moisture in the low to mid levels and dry air aloft. By aftertoon, numerous heavy thunderstorms pop up.

Which shows the "water vapor" sattelite can be very deceiving. Its a great tool for osberving anything in the upper levels, such as short waves and jet streams.

Bravo!
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70 knots surrounded by flagged data...withholding opinion for the moment.

http://tropicalatlantic.com/recon/URNT15/KNHC/
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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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IDa on NOLA Medium Range Radar

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The last two recon fixes show the center heading right for the HH home air port in Biloxi.
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Please don't blast me, but if you do its still ok. Everyone in Ida's path keep safe, she packs a bigger punch than most might think, if she takes that ESE movement the whole west coast of Florida could have a much bigger impact, jmo
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505. Halyn
I just got here .. has anyone heard from Oz and/or Ike ??
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Quoting atmoaggie:

One more: there can be attenuation of the radar beam by an area dense with hydrometeors, giving a distorted view, or none at all, of precip beyond the high density stuff.
Sometime today, there may be features visible on the New Orleans long range radar, not visible via Mobile's radar because of this.

Water vapor by satellite obviously does not have this issue.



The one issue with the water vapor sattelite image, is it only gives you an example of the upper atmospheric situation.

For Example, many times we have had 2.00 + PWAT air where there is deep layer moisture in the low to mid levels and dry air aloft. By aftertoon, numerous heavy thunderstorms pop up.

Which shows the "water vapor" sattelite can be very deceiving. Its a great tool for osberving anything in the upper levels, such as short waves and jet streams.
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Quoting atmoaggie:
This does look to be a little bigger in the TS-force wind area. Caveat: This product depends on some persistence between the time of satellite pass and production of this product. Can be off in a fluid situation such as Ida with much latency in the satellite data.



Okay is orange TS winds?
Member Since: September 6, 2009 Posts: 2 Comments: 3710
I'll change my name to BessieBurger if someone will acknowledge my lowly and uninformed questions:). Possible flooding in NO, TWC showed projected water/surge in that area and is Ida the last hurrah of 2009 or other activity to follow.
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IDA is a tenacious little bugger. Stumping the best of em.
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Quoting NRAamy:
do we have two tacos now?

where is burritoMan?

ChimichangaChick?


No I'm the "Real" Taco here in Mobile AL LOL
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Ida will not make landfall in FL. IMO
Xtra,Xtra,read all about it..

LOL

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If you look on the visible Sat on this site,its easy to pick out, that this storm is still moving NNW!
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Quoting Thundercloud01221991:
Recon found 70 knt surface wind



May need to dust off the flags once again for unpredictable IDA.
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989.9 mb
(~ 29.26 inHg)

SFMR
70 knots
(~ 80.5 mph)
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do we have two tacos now?

where is burritoMan?

ChimichangaChick?
Member Since: January 24, 2007 Posts: 317 Comments: 31946
Wind is finally picking up a bit on the West end of Panama City Beach. Take a look:
Backyard Webcam( w/some tunes...
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Recon found 70 knt surface wind
Member Since: August 1, 2006 Posts: 28 Comments: 3716
Quoting stormsurge39:
Is Ida suppossed to turn at all to the East before landfall? If it doesnt, its going in at Mobile or a little west of Mobile!


With the current Speed she is at right now, That would not surprise me at all....

Good to see you StormSuge
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Looking @ RGB it appears further strengthening is underway for IDA.
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Is Ida suppossed to turn at all to the East before landfall? If it doesnt, its going in at Mobile or a little west of Mobile!
UPDATE POSTED:
South Florida StormWatch
(main site)
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That needle you speak of is where a lot of us live.
Oh, yeah we do!

So we may see the original track for a landfall after all.
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Link i believe this link has all the latest road closures for the state of alabama. confirms DI bridge being open
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Quoting VIPForecastor:
My prediction after looking at the water vapor loop provided by NOAA and the Gulf Infrared Satellite loop. I must say that it appears that the storm has already turned North.

I forecast somewhere between Mobile, AL and Crestview, FL. But, it looks to be close to the AL/FL line to around Gulf Breeze area.


Don't go out on a limb now...
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There is the reason for the virga...it was evaporating (and cooling the air) in the dry layer from 600 to 850 mb. (Notice the cooler than above air temps around the 600 mb height)

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Quoting P451:
The scope of this merging of multiple systems is just impressive.



This is what happens when a EPac invest (96E) merges with a Hurricane (Ida) merges with a hybrid extratropical system (BOC system - south of LA right now - still an ongoing process) merges with a trough (that swept in from Mexico) merges with an ULL (that swept through western Texas yesterday)

Pretty wild scenario that came together here. Mother Nature putting on a show.


Lets see what this does for us in the NE. We have had a high level overcast all day and warm temp.

Also watching the Recon and the entire NE portion of Ida has greater than 60 mph surface winds
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Quoting Wetagain:
The report of dauphin island bridge being closed was premature. Just rode it and the causeway. Wind driven spray on roadway - for now. D I police confirmed town does not close it- state calls and tells them to. No info as yet from state to close. Was pretty gusty tho that high up in a suv.


Just wondering if you could get to the west end of the Island..... I have heard that it was under water already....

Taco :0)
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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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