Hurricane Humberto

[Mike Umscheid]

One word that is missing in almost all of Rob Dale's arguments is "maximum" before the word "sustained". Sure, while many of the observations recorded sustained winds below "maximum", who is to say that 1-minute winds higher than what was recorded by widely spaced instrumentation didn't occur a mile away...or even 100 yards? I am reminded of a recent microburst here at the KDDC airport several weeks back. The northside of the Runway 14, where the ASOS is located, recorded a a 73mph gust, while here at the office ("NWS" on that PDF link), we maybe hit 45mph peak gust at our building, if that, about 1/4 mile away. At the time it occurred, I thought the ASOS unit was broken or something, because looking out the window, I can surely attest that the winds were not even close to 73mph in gusts. I was flabbergasted! Obviously a completely different meteorological phenomenon, but it illustrates the point that pockets of higher surface winds can and do go unmeasured (or measured in my example!). This is why when it comes to landfalling hurricanes, the use of WSR-88D velocity data, in my opinion, is so very crucial in realtime operations and post-analysis.

 

[Scott Overpeck]

Wow, this thread has gone in a few different directions. First, let me clear a couple of things up. First, High Island, TX is in Galveston county just south of Chambers county, part of the Houston CWA. Galveston Co includes Bolivar up to through Gilchrist and High Island. They are just a couple of miles west of Jefferson Co which is where Lake Charles CWA begins. Humberto made landfall somewhere close to High Island, likely on the border of Galveston/Jefferson Co or on the border of Houston and Lake Charles CWA.

Second, having gotten more aerial photographs from the Galveston Co EM, we've been able to better evaluate the wind speeds from the damage Humberto caused. This was recently increased to 70-80mph with gusts to 90mph. I'll address the reasons for this in another post as I just wanted to get this out quick.

 

[Scott Overpeck]

Well, I’ve address a couple of items already. I’ll pick up on the wind speed estimates from the damage survey. We did the survey on the ground unable to get to areas east of Winnie and High Island where the high wind speed likely occurred. At first glance, the damage did not look that impressive mainly for a couple of reasons. First, construction of buildings in these areas was very poor and anything well built had little if any damage. Homes that did have damage were poorly built. There were quite a few trees uprooted, but there was also quite a bit of rainfall in the area leading to saturated grounds. This would make it easier for trees to uproot. Unlike tornadoes, the duration of wind speed also has to be considered. Looking at the damage, we found several damage indicators that would support 100 mph winds based off the EF damage scale. These indicators would be mainly significant damage to roofs, trees uprooted, but also well built power poles that were snapped. Again, this would indicate winds near 100 mph. We went on the low end of the wind speed based on these indicators mainly because of the poor construction and saturated ground. We went low also because of the long duration of 20-30 minutes of near hurricane strength or lower winds. We went too low at first. We finally got some aerial pictures of the damage from the Galveston Co EM with damage we had not seen. These pictures helped support raising the estimated winds speeds from the damage from 60-70 G 80 mph to 70-80 G 90 mph. The duration of the winds and the poor construction played a big role in estimating the wind speeds from the damage, different from estimating the winds from tornado damage.

I have also been able to go back and look at the radar data. If you want to look for yourself, download the level 2 data from NCDC and pop it into GR Analyst 2. We just got done archiving the AWIPS data and we’ll look at that as well. But just looking at the level 2 data in GRAE2, when the storm made landfall there were Doppler velocities around 85kts inbound over a broad area of High Island in the north eye wall. This was around 0610Z. About 15 minutes later, there were Doppler velocities inbound at around 105kts, again just east and northeast of High Island. Granted at this time the radar beam is about 3Kft above the ground, but this supports the hurricane aircraft reports of 98kts. So, is an 85 mph maximum sustained winds too much? Personally, I think it is very much in the ball park and a good estimate based on what data was available at the time. There is virtually nothing between High Island and Beaumont, so no way of knowing for sure.

I don’t think NHC over doing wind speeds is that much of an issue especially when you have good radar data (eye of storm was about 50nm from the HGX radar) and good aircraft measurements. Plus, you have to realize these products are not just for the public. Emergency management and FEMA use them also. Just about every emergency manager I know wants to know the worst case scenario, and what is the worst that can be expected. So if over doing wind speeds some to help out the emergency management plan rescue efforts and get needed supplies in place after the event, then I think that is well worth it. So, yes I agree we need to scrutinize the data and get the science right, but when it comes to the forecast and getting information out that can save lives, I think we can all live with a little overestimation of wind speeds especially when you have quality data to use despite a poor surface observation network. Further inland, again, this may be where the data needs to be re-evaluated and learned from. But, I still believe in making the best forecast you can with the data you have available and using situational awareness as needed to adjust. I think we also need to go back and look at the data to make sure we understand the science so we can make better forecasts next time. Post mortems are important in that aspect. I’m sure we as well as NHC will be looking at this case to learn as much as possible.

Sorry for the long post, but I finally got my thoughts together on this after a few days.

 

[rdale]

Thanks for the details.

 

[JR Hehnly]

After reading of the damage in the area, coupled with radar evidence, I have come to the realization that I was mistaken in my disbelief of the wind estimates. Apparently there is still much for me to learn concerning this. I'd like to apologize to those individuals and organizations I have criticized unjustly, and thank all those who posted to help explain something that I didn't understand.

 

[Josh Morgerman]

Interesting thread. To me, the surface obs for Humberto were not at all surprising given the cyclone's estimated intensity of 75 kt (1-min) and its size. As Jack Beven points out, the inner core was very small. The right-front quad passed over a completely empty section of the coast-- between High Island and Sabine Pass-- where there is nothing.

The BPT observed max wind at ~1000Z (47 kt with a gust to 73 kt) perhaps seems a bit low, given that that station was in the N eyewall and the advisory intensity one hour before (0900Z) was still 75 kt. However, as we all know, winds within the eyewall of even a severe hurricane vary greatly from quadrant to quadrant. Just being in the eyewall doesn't mean you'll necessarily experience winds anywhere near the maximum. In fact, it would take a very simplistic view of a hurricane's wind field to assume that you'll experience the maximum (or "best-track") wind just because you're in the eyewall. As Rich Horodner pointed out above, it's way more complex than that, and-- even in the eyewall-- the max winds are localized and streaky.

I have no opinions Re: Humberto's landfall intensity-- I defer to the experts. My only point is that you can't insist on surface obs substantiating landfall intensity-- they never do, because, unfortunately, an official reporting station is almost never perfectly situated right on the open coast, in the absolute highest isotach.

 

[Derrick Herndon]

Case in point is Typhoon Wipha (13W) which just plowed through the Ryuku Islands. The eye passed over 2 stations and the eyewall hit possibly 2 other stations. None of these stations reported winds > 85 kts sustained (highest is 39 m/s) and yet this storm has an estimated intensity of 100-140 kts and was very impressive on radar passing over the islands. The lowest pressure reported by Iriomotejima was 928 mb with winds of 10 m/s at the time. So for some storms you can get a good idea of the MSLP from the obs but the MSW can be tough to nail down from the obs. Given nearby obs you could estimate the gradient wind but it would only give you the minimum sustained wind unless the obs were perfectly positioned throughout the eyewall.

 

[Scott Overpeck]

Just let everyone know, we have a preliminary summary of Humberto on the webpage.

We have a screen shot of GRAE2 with Humberto making landfall and some damage photos. Enjoy!

HGX Humberto summary

 

[Josh Morgerman]

Just let everyone know, we have a preliminary summary of Humberto on the webpage.

We have a screen shot of GRAE2 with Humberto making landfall and some damage photos. Enjoy!

HGX Humberto summary

Cool summary-- very interesting to read. Thanks for sharing it!

One question: it mentions a zone of 60-70-kt winds occurring from just E of Canal City to 6 mi N of High Island. Given that the landfall point was just E of High Island, wouldn't winds have been a bit stronger along that desolate stretch of coast between High Island and Sabine Pass?

 

[Scott Overpeck]

Josh - the 60-70kts (70-80mph) wind estimates were based off the damage seen from Canal City to High Island. Hwy 87 that runs along the coast is closed east of High Island, so no way of knowing what the winds could have been like since we can't get to any damage. The aerial survey did not go into Jefferson Co either. The area from Canal City to High Island caught the northern to northwestern eye wall which caused the damage there. I suspect that if there was something to hit or a sfc ob, we would have gotten higher winds in that area. Just nothing there to know. Kinda like a big wedge tor in the TX panhandle in the middle of a field that hits nothing.

 

[Josh Morgerman]

Josh - the 60-70kts (70-80mph) wind estimates were based off the damage seen from Canal City to High Island. Hwy 87 that runs along the coast is closed east of High Island, so no way of knowing what the winds could have been like since we can't get to any damage. The aerial survey did not go into Jefferson Co either. The area from Canal City to High Island caught the northern to northwestern eye wall which caused the damage there. I suspect that if there was something to hit or a sfc ob, we would have gotten higher winds in that area. Just nothing there to know. Kinda like a big wedge tor in the TX panhandle in the middle of a field that hits nothing.

OK, gotcha. I misread the report to be implying that the max winds occurred in that zone (E of Canal City to 6 mi N of High Island). Thanks for the clarification.

 

[Ed Schoenborn]

Hernando chased me on Sep. 14 with two tornadoes. Ed

 

[Ed Schoenborn]

Touche! I was chased by the remnants of Hurricane Humberto with two torndoes one in Johnston County and the other in Cumberland County Sep. 14, 2007 both in North Carolina.

 

[Danny Neal]

LoL, do you mean Humberto? There was never a Hernando this year.....

Touche! I was chased by the remnants of Hurricane Hernando with two torndoes one in Johnston County and the other in Cumberland County Sep. 14, 2007 both in North Carolina.

 

[Ed Schoenborn]

Thanks Daniel for correcting me. I did mean Humberto not Hernando. Now, how do I edit my initial post?