Max wind distribution in Ike / other canes

[Tim Vasquez]

This morning when I was waking up I was thinking about the wind distribution in Ike, so I sat down and made these composite maps of the 0.5 deg radar reflectivity with the NOAA/AOML "max 1 min sustained wind product" this link at the time of landfall (0730 UTC).

I'm not sure if there's much to be gained from the base velocity image since it's hard to tell what the orientation of the wind field is with respect to the radar.

As far as reflectivity, I expected the highest winds to be on the inner edge of the eyewall (for example, near that yellow fragment about to come ashore near Crystal Beach) since the fastest movement of reflectivity elements seemed to be there. However AOML's analysis suggests the highest winds are embedded in the middle of the eyewall.

Also AOML's analysis of max wind does not follow the eyewall shape at all offshore and on the western aside. Should we be taking AOML's analysis as the most accurate guess? Smoothing error? Anything we can learn about figuring the radius of max wind?

Tim

 

[Tim Vasquez]

Also to add to my previous post, this was my mental conceptual model of the max surface wind distribution Friday night (crappy art job... I need a Wacom tablet). Should it not be like this?

 

[Jeff Snyder]

Also AOML's analysis of max wind does not follow the eyewall shape at all offshore and on the western aside. Should we be taking AOML's analysis as the most accurate guess? Smoothing error? Anything we can learn about figuring the radius of max wind?

Tim

Tim,

I think the expanse of the wind max to the northeast of the eye was supported by Recon data, which showed the area just offshore from the Bolivar peninsula to near Port Arthur as having sfc winds above 75 kts (sustained 80-90 kts in places), with the peak winds (IIRC) at the sfc located just NE of the Bolivar peninsula. In addition, there was a dropsonde measurement of 118 kts at 360 m (925 mb) offshore between Port Arthur and the Bol. peninsula near High Island (or maybe even NE of that). If those data are correct then the analysis doesn't look too bad. I think the highest METAR I saw was from KBPTat 55-60 kts sustained gusting to 75-80 kts, but I don't recall the exact numbers. Obs from that site seemed close to what KHOU was reporting before they stopped reporting the wind, and KHOU was in the inner eyewall while KBPT was farther away. Suffice it to say, I haven't seen any SFC obs that would have been able to sample the strong winds near High Island (though, as noted by either J. Beven or someone else in the Ike thread, there is some hope that perhaps there was a research station or two up there).

That said, it did look like Mike Bettes (in Clear Lake where he measured 98 and 101 mph wind gusts) saw some higher winds than what that analysis indicates. Perhaps the AOML analysis is limited in the resolution, and thus gradients, that they are able to draw...? I mean, I would think that the gradient from wind max in the eyewall to weak winds in the eye may be a bit stronger than the analysis shows. In addition, I've always thought that the drop from over-ocean to over-land wind speeds was more several than indicated.

Regardless, neat analysis - radar overlay! Thanks!

EDIT: It would have been neat to have seen KHGX in the middle of the eye. In such an orientation, the radar should have sampled only the Ike-relative radial component - i.e. the convergent component of the storm - instead of the strong azimuthal/tangential/rotational wind component that can greatly exceed the radial-inward component. I wonder if the HGX radial velocities would have been higher over land than over the ocean since frictional effects may have allowed for a greater inward wind (relative to the center of the storm) over land than over water, at least in the areas for which gradient wind approximation holds (i.e. not in the immediate eyewall, where, AFAIK, the flow is in cyclostrophic balance more than gradient wind balance). Has the center of a hurricane eye ever moved directly over an 88D?

 

[IAN GIAMMANCO]

Just a quick blurb about the Hwind products. Hwind assumes marine exposure over water, or a Zo of 0.01 m whereas over land it is assumed to be 0.03 m. There is quite a bit of speculation regarding roughness lengths at the immediate shoreline.

 

[Justin Walker]

Has the center of a hurricane eye ever moved directly over an 88D?

Hey Jeff,

I am not a tropical historian, so I can't answer this question directly, but we had DOW6 in Galveston for Ike and came very, very close to being dead center in the eye. So we came very close to measuring the Ike-relative radial component. Josh has a preliminary little pdf (actually not little in size, 12mb's) on the http://www.cswr.org website. We stopped running a staggered prf and set the nyquist down to 12m/s. There are some very cool mesovortices rotating around the eye. We are making a movie loop of the eye with the DOW radar, but the file size is 1.7 gb's....so we need to compress that a bit!

We had two mobile mesonet vehicles and also brought our tornado pods and deployed five in Galveston and five in Texas City on the sea walls. Our highest gusts were right around 100mph. If you are patient, and download the pdf; you can see our deployment locations, radar images and some preliminary pod plots.

 

[rdale]

Justin - thanks for pointing the summary! Shocked to see it so fast...

One note - the timestamps are wrong unless my math is off, 7Z is converted to 1am CST and that should be either 1am CDT or 8Z? One of those is incorrect on every map.

 

[Justin Walker]

Yup...you are correct. The z times are the correct times but we just converted wrong, we will try to fix that or just put a note up.

Justin - thanks for pointing the summary! Shocked to see it so fast...

One note - the timestamps are wrong unless my math is off, 7Z is converted to 1am CST and that should be either 1am CDT or 8Z? One of those is incorrect on every map.

Also, we have looked over our instrument data a little more now and the Pod we deployed on the causeway into Galveston (Pod F), had a 1 sec gust of 51 m/s (~112 mph). The max 1 minute sustained wind with Pod F was 32.5 m/s (~72 mph). The surprising thing is that the Pod on the causeway did not have the highest sustained wind even though its elevation is dramatically higher than the other pods. Our highest overall 1 minute sustained wind was Pod C on the Texas City seawall with 36.2 m/s (~80 mph) with a 1 sec gust of 44 m/s (~97 mph).

-Justin

 

[IAN GIAMMANCO]

Justin, I would caution you about data on elevated surfaces as well as anywhere with topographic speed up effects, there are some good methods for accounting for this though. We encounter the same things with the Stick-Net probes since we can get them in far more remote locations than the older 10 m WEMITE towers.

On a second note, retrieved the probe on Ft. Travis at the western end of the Bolivar, at 2.25 m height peak instantaneous gust was 88 mph, peak 3-sec was 87.0 and sustained (1-minute mean) of 73.4. Probe was pretty much marine exposure. Interestingly the northern and southern eyewalls were of comparable intensity. I think HWind is on the money though with its depiction of the wind max in Chambers Co.