An Eyewall Replacement Cycle of Hurricane Igor

By: 1900hurricane , 3:51 PM GMT on September 14, 2010

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It appears that Igor did have an Eyewall Replacement Cycle yesterday/last night, and it did catch the NHC off guard. It was a rather subtle one, but it affected Igor's strength the same. Here are some 85GHz Microwave passes to show it's evolution:



SSMIS Pass @ 2245 UTC September 12th: Hurricane Igor is rapidly intensifying and screams past the threshold for a category 4 hurricane and threatens category 5. At this time, Igor's core is amazingly consolidated and probably in it's most efficient form, which is what allowed the rapid intensification in the first place. Igor is displaying the features of a mature hurricane.



SSMIS Pass @ 11:19 UTC September 13th: Hurricane Igor has reached maximum intensity. At this time, he is just 10 kts shy of the category 5 threshold. However, Igor's intensification levels off here. In the pass above, it can be seen that his core is not as perfectly structured as before and the thickness of the return maximum has increased. This is a sign of some type of internal change, and the widening of the return maximum means that individual storms close to the eyewall have increased in intensity. With the diffusion of the strength in his core, Igor can no longer strengthen.



AMSRE Pass @ 16:40 UTC September 13th: Igor's core has continued to undergo changes, and by this time, a secondary return maximum has developed outside the eyewall. This signifies that the intense storms close to Igor's eyewall have continued to develop and formed a secondary eyewall. I estimate that an Eyewall Replacement Cycle (ERC) has started to begin at this point. This can also be hinted at in infrared imagery as Igor's cloud tops began to cool, especially those directly adjacent to his eye.

However, at this time, the NHC seemed to disregard the dual return maxima and possible ERC when they stated in their forecast discussion:

WHILE A 1640 UTC
AMSR-E PASS DOES NOT SHOW ANY EVIDENCE OF A SECONDARY EYEWALL
YET...IT IS POSSIBLE THAT AN EYEWALL REPLACEMENT CYCLE WILL OCCUR
IN THE FIRST COUPLE OF DAYS...WHICH COULD RESULT IN SOME INTENSITY
FLUCTUATIONS NOT REPRESENTED IN THE OFFICIAL FORECAST.

However, the trends continued with the next couple of passes:



TMI Pass @ 20:36 UTC September 13th: This pass basically shows an extension of the earlier AMSRE pass and continues to show the evolution of the dual return maxima and progress of the ERC. At this time, it appears that the outer eyewall is becoming the dominant.



SSMIS Pass @ 22:27 UTC September 13th: Once again, the trend continues and it appears that the outer eyewall is circling in and trying to take the same place as the collapsing inner eyewall. By now, the ERC is entering its final stages.

After these couple of passes as well as the continuing trend of Igor's cooling cloud tops, the NHC had this to say in their forecast discussion:

MICROWAVE AND GEOSTATIONARY SATELLITE IMAGERY SUGGESTS THAT AN
EYEWALL REPLACEMENT CYCLE MAY HAVE BEGUN. TRMM...WINDSAT...AND
SSMIS PASSES FROM ABOUT 5-6 HOURS AGO ALL INDICATED THAT A
SECONDARY EYEWALL WAS BEGINNING TO FORM...AND MORE RECENTLY
CONVECTIVE TOPS AROUND THE EYE HAVE BEEN WARMING.

It appears that they had finally caught on.



TMI Pass @ 04:48 UTC September 14th. By now, the inner eyewall has collapsed and the outer eyewall has taken over, which can be seen in the reconsolidation of a single return maximum at the eyewall. Also of note is the enlarged eye this pass. Igor's ERC is complete and subsequently, his cloud tops began to cool once more.

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19. 1900hurricane
6:09 AM GMT on September 16, 2010
It'll be interesting to see what we have here in the morning regarding both Igor and Karl.

Member Since: August 2, 2006 Posts: 46 Comments: 11666
18. 1900hurricane
1:24 AM GMT on September 16, 2010
Quoting EmmyRose:
yup looks hurricanie to me....

Still going to Tampico.

Karl? Yeah, he still looks really good! I'm surprised actually how well he has held together.



Member Since: August 2, 2006 Posts: 46 Comments: 11666
17. 1900hurricane
1:23 AM GMT on September 16, 2010
And just for kicks, how about some GOES-15 IR to watch as the eye clears?



Click the image to view a loop.
Member Since: August 2, 2006 Posts: 46 Comments: 11666
16. EmmyRose
1:14 AM GMT on September 16, 2010
yup looks hurricanie to me....

Still going to Tampico.
Member Since: July 15, 2005 Posts: 347 Comments: 76405
15. 1900hurricane
1:00 AM GMT on September 16, 2010
And now we're just about done. It shouldn't be too much longer until Igor resumes strengthening.

Member Since: August 2, 2006 Posts: 46 Comments: 11666
14. 1900hurricane
11:01 PM GMT on September 15, 2010
If this isn't an ERC, then I don't know what is!

Member Since: August 2, 2006 Posts: 46 Comments: 11666
13. Barefootontherocks
8:11 PM GMT on September 15, 2010
12. 1900...
Way cool!

And good job on this blog.
Member Since: April 29, 2006 Posts: 151 Comments: 18360
12. 1900hurricane
7:53 PM GMT on September 15, 2010
Thanks Beell! Yeah, I've always wanted to do something with tropical cyclones, but I really am pretty sure now that I want to do research on the core and inner dynamics of them. Ever since I joined the blogs in 2006, that is what has fascinated me the most and I feel like some good research on them can be done. I'm particularly interested in rapid intensification and eyewall replacement cycles, which happen to be two of the least understood things in tropical meteorology!
Member Since: August 2, 2006 Posts: 46 Comments: 11666
11. beell
6:57 PM GMT on September 15, 2010
Great read and obs on the eywall, 1900.

Looks like a wide open subject that you seem to enjoy digging into. You're in good company!
Thanks.


HURRICANE IGOR DISCUSSION NUMBER 28
...IT IS LIKELY THAT INTERNAL DYNAMICS...WHICH ARE NOT WELL UNDERSTOOD...WILL INFLUENCE THE INTENSITY...

HURRICANE IGOR DISCUSSION NUMBER 29
...INTERNAL DYNAMICS WILL LIKELY BE THE DOMINANT FACTOR FOR THE FUTURE INTENSITY OF IGOR FOR THE NEXT COUPLE OF DAYS. THESE SMALL SCALE DYNAMICS...WHICH ARE NOT WELL UNDERSTOOD...

HURRICANE IGOR DISCUSSION NUMBER 30
...FLUCTUATIONS IN INTENSITY ARE LIKELY TO BE GOVERNED BY INTERNAL DYNAMICS FOR WHICH PREDICTABILITY IS POOR...
Member Since: September 11, 2007 Posts: 141 Comments: 16213
10. 1900hurricane
6:41 AM GMT on September 15, 2010
And here is the structure of the rapidly-intensifying Julia:

Member Since: August 2, 2006 Posts: 46 Comments: 11666
9. 1900hurricane
6:29 AM GMT on September 15, 2010
It appears that Igor may be undergoing another ERC, with this one being much less subtle!

Member Since: August 2, 2006 Posts: 46 Comments: 11666
8. EmmyRose
9:59 PM GMT on September 14, 2010
THE SYSTEM IS UPGRADED
STRAIGHT TO TROPICAL STORM KARL
Member Since: July 15, 2005 Posts: 347 Comments: 76405
7. EmmyRose
8:15 PM GMT on September 14, 2010
Tampico?
Member Since: July 15, 2005 Posts: 347 Comments: 76405
6. 1900hurricane
8:02 PM GMT on September 14, 2010
Well, this is impressive and unexpected!

Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 14th day of the month at 19:45Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 305)
Mission Purpose: Investigate fourth suspect area (flight in the North Atlantic basin)
Mission Number: 1
Observation Number: 10
A. Time of Center Fix: 14th day of the month at 19:24:50Z
B. Center Fix Coordinates: 18°10'N 83°55'W (18.1667N 83.9167W)
B. Center Fix Location: 183 miles (295 km) to the WSW (245°) from George Town, Cayman Islands (GBR).
C. Minimum Height at Standard Level: Not Available
D. Estimated (by SFMR or visually) Maximum Surface Wind: 56kts (~ 64.4mph)
E. Location of the Estimated Maximum Surface Wind: 10 nautical miles (12 statute miles) to the S (176°) of center fix
F. Maximum Flight Level Wind Inbound: From 255° at 27kts (From the WSW at ~ 31.1mph)
G. Location of Maximum Flight Level Wind Inbound: 13 nautical miles (15 statute miles) to the S (176°) of center fix
H. Minimum Sea Level Pressure: 1004mb (29.65 inHg) - Extrapolated
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 20°C (68°F) at a pressure alt. of 214m (702ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 25°C (77°F) at a pressure alt. of 212m (696ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 24°C (75°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature
N. Fix Levels (sfc and flt lvl centers are within 5nm of each other): Surface and 1,500 feet
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 1 nautical mile
Remarks Section:
Maximum Flight Level Wind Outbound: 34kts (~ 39.1mph) in the northeast quadrant at 19:32:00Z
Sea Level Pressure Extrapolation From: Below 1,500 feet

Not only is the winds very impressive, but it was found south of and close to the center. This may because of a well-consolidated but small core associated with Karl. The fact that it was in the south may mean that it is rapidly strengthening.
Member Since: August 2, 2006 Posts: 46 Comments: 11666
5. EmmyRose
7:42 PM GMT on September 14, 2010
INVEST 92L

This tropical wave has moved into the eastern Caribbean Sea. While it bears watching -- and most of the intensity models develop it into a tropical storm -- the system appears likely to track across the Yucatan Peninsula, across the Bay of Campeche and into the Eastern Mexico coast.

For now, Houston may see a slightly elevated chance of showers this weekend from the storm, as well as choppy surf and tides 1 to 2 feet above normal. It's possible though unlikely the storm will take a more northerly path, bringing it closer to the Texas-Mexico border.
Member Since: July 15, 2005 Posts: 347 Comments: 76405
4. 1900hurricane
7:40 PM GMT on September 14, 2010
Pattern Change?
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3. EmmyRose
7:21 PM GMT on September 14, 2010
Bienvendios-
there goes my birthday weekend.

Photobucket
Member Since: July 15, 2005 Posts: 347 Comments: 76405
2. 1900hurricane
4:59 PM GMT on September 14, 2010
Hey Michael, thanks for stopping by! Yeah, the NHC has been confusing me slightly lately.

The CIMMS blog has a good entry up on Igor that mentions the ERC (albeit briefly) as well:

Link
Member Since: August 2, 2006 Posts: 46 Comments: 11666

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About 1900hurricane

Texas A&M meteorology major; hardcore weather enthusiast. Class of 2013 (+ a victory lap or two). My raw passion for extreme weather is hard to match.m@