Hurricane Alex

[cdcollura]

Good day all,

With such a low pressure - Theoretically - Alex SHOULD be a strong cat-3 hurricane. But it's not, and here's why...

The storm moved over land, and if anyone remembers Ike in 2008, after it's Cuban landmass crossing, it had a pressure fall that would make a strong cat-4 but was barely a cat-2 and remained that way for a while despite crossing favorable warm waters.

The thing here is the core of the system is large and expansive (not as big as Ike, but big, nevertheless). This is why the pressure is so low, but the winds do not justify such low pressure. Like an ice skater with her arms out, Alex is just that, and all the energy is focused on multiple wind maximas around a large system, and not "concentrated" in one single eyewall. Ike was very similar to this.

Similar to Ike, Alex should continue deepening, and slowly recover from its treacherous "land crossing" and re-constitute it's core flow about a tighter path. I see a low end cat-2 during it's landfall Wednesday night / early Thursday morning.

Also keep in mind that when there is a sudden / significant pressure drop, the winds do NOT immediately reflect that because of inertia. It takes time for acceleration to occur with the increased pressure gradient (and the opposite is true when the storm winds down).

Finally, the environment around Alex is a bit low in pressure, accounting for a shallower gradient. But this does not affect the core flow very much, so the multiple wind maximas indicate the kinetic energy is spread out for now.

Note: With the large wind field associated with this storm (large gale / TS wind envelope around the hurricane forced winds) will create a storm surge / high waves equivalent to a cat-3 or more (10-15 feet surge or so) ... And these conditions will arrive LONG before the storm core does, possibly when the sun is still out (remember Ike)? - Keep that in mind when chasing in Mexico.

Above is an interesting comparison to the pressure "structure" of Hurricane Ike in 2008. The very large wind field and pressure "curve" shows a system with multiple speed maximas and "spread out" wind energy, despite the pressure being that of a storm that should be at least 2 categories stronger.

Above: A "typical" wind and pressure structure of a "normal" hurricane with the same pressure as Ike in the last example above. The tighter core flow makes for a wind speed more typical of such low pressure.

 

[Zach Young]

Looks like Alex is becoming more organized. It's beginning to present an eye on visible satellite (IR eye is a bit less pronounced)

MODS: Perhaps the title of the thread should be Hurricane Alex?

 

[cdcollura]

Good day all,

Interesting as it appears a central "core" and eyewall / eye has developed around the system as per visible satellite and around that appears to be a "moat" region (less clouds) surrounded by another ring of weaker convection.

Still stinks that Josh M and other(s) chasing this have to deal with a night-time landfall ;-(

 

[Marko Korosec]

Pretty impressive radar presentation from Brownsville, TX radar site:

 

[cdcollura]

Good day all,

Clearly a double / concentric eyewall system.

As I mentioned earlier based on the visible satellite, a moat is clearly evident around the inner eyewall and inside the outer (weaker) eyewall on the radar presentation by Marko K as well.

Landfall should be at about the 8-10 PM time-frame, locally (CDT).

 

[Jared Thompson]

This is the lastest radar and wind field scans. The eastern eye wall has 91 knot wind speeds at BV 0.5 really intresting to see if it will get any stronger before land fall

 

[cdcollura]

Good day all,

I was looking on GRLevel3 and see Jeff Gammons in S Padre Island - Good luck if he's there, but he is a bit far from the core flow / hurricane winds. He's probably getting winds / waves, though.

I was suprised as I saw SN showing Jeff G, and Doug K for a while, but I doubt any of theme are near there.

Anyway, Alex is close to making landfall in roughly 3 hours, and wobbled to the left, then back to the right on the last few scans from KBRO. It's a general due-West motion if you squint / remove the "wobbles".

 

[Greg Blumberg]

Apparently per the dropsonde observations, Alex has been upgraded to a CAT 2 with 950 mb central pressure, and the wind speed around 100 mph.

http://tropicalatlantic.com/recon/UZNT13/KNHC/

 

[cdcollura]

Good day all,

Hurricane Alex's western eyewall (100 to 105 MPH winds) is just impinging on the Mexican coastline.

Hold on, fishermen!

 

[Robert Rohloff]

NHC advised the eye wall crossed onto land around 2100 hrs CDT. For the first system of the Atlantic season this was a significant start, I wonder what the peak season will bring.

 

[Rich Thompson]

I suspect Alex was very nearly a major (CAT 3) hurricane at landfall given the continued pressure falls (down to 947 mb) and the improving radar/satellite presentation all the way through landfall. The KBRO radar sampled 110-120 kt peak velocities at about 13 K ft, which translates to 100-105 kt at the surface using a reduction factor of 85-90% (probably not too bad given the convective structure of the core). The radar structure suggested a 10 mi diameter eye with ~10 mile width eyewall containing the hurricane conditions.

I'll be curious to see how NHC handles this one in the post-event analysis, though they could just stick with the 90 kt estimated max winds.

 

[Jack Beven]

I suspect Alex was very nearly a major (CAT 3) hurricane at landfall given the continued pressure falls (down to 947 mb) and the improving radar/satellite presentation all the way through landfall. The KBRO radar sampled 110-120 kt peak velocities at about 13 K ft, which translates to 100-105 kt at the surface using a reduction factor of 85-90% (probably not too bad given the convective structure of the core). The radar structure suggested a 10 mi diameter eye with ~10 mile width eyewall containing the hurricane conditions.

I went off duty before those doppler winds appeared (I saw winds up to 90 kt at 10000 ft through 23Z), so I'm not sure where they were in relation to our aircraft winds. However, winds measured by the aircraft at 5000 ft and surface winds estimated by the Stepped Frequency Microwave Radiometer don't seem to support much more than what we carried in our advisories.

Jack Beven

 

[Josh Morgerman]

Hi, folks! My chase partner, Jorge Gonzalez, and I chased Alex up into remote Tamaulipas and rode out the cyclone in Guadalupe Victoria. Although we had access to no information or data, we had the impression that we got a bullseye hit.

The winds and rain preceding the center had an odd, pulsing quality-- increasingly frequent bursts of energy separated by mellower periods. The eye came later than we expected, but very suddenly around half past midnight. The drop-off to a dead calm was swift, and the lull was short-lived-- perhaps 20 mins. Although it was dark, Jorge and I believe we could see the curved wallcloud of the inner eyewall. (Too bad video could not pick up these details.) The backside swept in as suddenly, and it was much more severe than the front. We were surprised by this, especially given that the last radar shots we saw prior to losing communication showed that the front (W) eyewall was much more robust. The wind really howled. However, the back eyewall was quite narrow-- within 30 minutes it was easing. Jorge and I estimated Cat-1 surface winds, although keep in mind we were in complete darkness, so it was hard to see what was happening. We found the road out of town when winds slackened to a low-end gale. (This is all from memory. When I review my timestamped footage, I´ll have more precise obs Re: when the eye occurred, how long it lasted, etc.-- and I´ll be sure to send these obs to Jack Beven. )

From the ground, the most distinctive feature of this cyclone was the very tight core. The periods of max winds before and after the eye were relatively brief, and the eye was very sharply defined-- almost freakishly so-- with the winds dropping off with a machine-like suddenness, and then increasing again with the back eyewall just as suddenly. We assume the eye was quite small, given how short the lull was. In light of the core´s daintiness, we were grateful to be so precisely situated for it. This was a microcane. Despite this, Jorge points out that the radius of gale winds was quite large-- based on what we´re seeing on our drive back to Monterrey (via Ciudad Victoria), it seems a huge swath of NE MX had damaging winds and floods. So it was a microcane embedded, like a jewel, in a much larger cyclonic gyre.

Re: video footage... Guadelupe Victoria was already completely blacked out before the arrival of the cyclone´s core, so this unfortunately limited the options to get good shots. However, I´ll be be posting the highlights on my Website within a few weeks, once I can sit down and go through it all.

 

[cdcollura]

Good day all,

... So it was a microcane embedded, like a jewel, in a much larger cyclonic gyre ...

That was the "double" / concentric eyewalls, the inner one is very intense when a rapidly intensifying hurricane is making landfall.

Glad you were on it, rolled the dice, and got "something" nice.

 

[Boris Konon]

Good day all,

With such a low pressure - Theoretically - Alex SHOULD be a strong cat-3 hurricane. But it's not, and here's why...

The storm moved over land, and if anyone remembers Ike in 2008, after it's Cuban landmass crossing, it had a pressure fall that would make a strong cat-4 but was barely a cat-2 and remained that way for a while despite crossing favorable warm waters.

The thing here is the core of the system is large and expansive (not as big as Ike, but big, nevertheless). This is why the pressure is so low, but the winds do not justify such low pressure. Like an ice skater with her arms out, Alex is just that, and all the energy is focused on multiple wind maximas around a large system, and not "concentrated" in one single eyewall. Ike was very similar to this.

Similar to Ike, Alex should continue deepening, and slowly recover from its treacherous "land crossing" and re-constitute it's core flow about a tighter path. I see a low end cat-2 during it's landfall Wednesday night / early Thursday morning.

Also keep in mind that when there is a sudden / significant pressure drop, the winds do NOT immediately reflect that because of inertia. It takes time for acceleration to occur with the increased pressure gradient (and the opposite is true when the storm winds down).

Finally, the environment around Alex is a bit low in pressure, accounting for a shallower gradient. But this does not affect the core flow very much, so the multiple wind maximas indicate the kinetic energy is spread out for now.

Note: With the large wind field associated with this storm (large gale / TS wind envelope around the hurricane forced winds) will create a storm surge / high waves equivalent to a cat-3 or more (10-15 feet surge or so) ... And these conditions will arrive LONG before the storm core does, possibly when the sun is still out (remember Ike)? - Keep that in mind when chasing in Mexico.


Above is an interesting comparison to the pressure "structure" of Hurricane Ike in 2008. The very large wind field and pressure "curve" shows a system with multiple speed maximas and "spread out" wind energy, despite the pressure being that of a storm that should be at least 2 categories stronger.


Above: A "typical" wind and pressure structure of a "normal" hurricane with the same pressure as Ike in the last example above. The tighter core flow makes for a wind speed more typical of such low pressure.

Wow...great explanation and graphics! Here's my $.02 I posted on another
forum. Thoughts?

----------------------

Alex shows once again the rather larger disparity between winds and central pressure that
can exist. Pressure as low at 958 mb and only 70 kts at one time? That is one of the lowest
pressures I think for such low winds speeds for a ATL system in the tropics. Ike in 2008
at one point was 65 kt at 966 mb, but that was after it was severely disrupted after its trek
across Cuba after being a Cat 4. Once this happened, I can see the pressure and wind being
out of whack a bit since the inner core gets disrupted. Isidore in 2002 was another good
example. It made landfall over the nrn Yucatan at 110 kts, meandered over land for about
a day, and emerged with its inner core completely disrupted. At one point the pressure was 980
mb but winds only 35 kts. It seems a lot of times a TC will have this disparity between its wind
and pressure after it loses it original "tightness" to its core from land influence in the tropics.
However, Alex crossing the Yucatan was still in a development phase and actually got better
organized while over land, so it is interesting that we had have this wind/pressure disparity
since it emerged into the Bay of Campeche.

This first really became apparent when Katrina made landfall at in the 920s but only had winds of 110 kts.
It is the primary reason I believe why pressure has been removed from the Saffir-Simpson Scale for categories.
We have seen a number examples since.

I wonder if the overall size of a TC has anything to do with this, Alex being a large system from the
start. Thing is though I don't believe there is any significant correlation to a TC's size and how
intense its core winds can get. Allen in August 1980 was the size of Alex in the same area
but had 160+ mph winds
http://upload.wikimedia.org/wikipedia/commons/5/54/Allen_08_aug_1980_1332Z_N6.jpg

 

[Boris Konon]

I suspect Alex was very nearly a major (CAT 3) hurricane at landfall given the continued pressure falls (down to 947 mb) and the improving radar/satellite presentation all the way through landfall. The KBRO radar sampled 110-120 kt peak velocities at about 13 K ft, which translates to 100-105 kt at the surface using a reduction factor of 85-90% (probably not too bad given the convective structure of the core). The radar structure suggested a 10 mi diameter eye with ~10 mile width eyewall containing the hurricane conditions.

I'll be curious to see how NHC handles this one in the post-event analysis, though they could just stick with the 90 kt estimated max winds.

Alex came very close to being the most intense ATL June hurr on record,
by central pressure anyways. Here is a list I put together awhile back.


MOST INTENSE ATLANTIC HURRICANES BY MONTH
**************************************

Max Wind Lowest Pres
June
AUDREY 1957 145 mph 946 mb

July
EMILY 2005 160 mph 929 mb

August
ALLEN 1980 190 mph 899 mb

September
GILBERT 1988 185 mph 888 mb

October
WILMA 2005 175 mph 882 mb

November
LENNY 1999 155 mph 933 mb

 

[Josh Morgerman]

I went off duty before those doppler winds appeared (I saw winds up to 90 kt at 10000 ft through 23Z), so I'm not sure where they were in relation to our aircraft winds. However, winds measured by the aircraft at 5000 ft and surface winds estimated by the Stepped Frequency Microwave Radiometer don't seem to support much more than what we carried in our advisories.

Jack Beven

Hi, Jack--

From my perspective on the ground, the 90 kt sounds about right.

I was in Guadalupe Victoria, directly in the path of the center, approx. 30 mi inland. (The 1 am CDT advisory position is right over Guadalupe Victoria, and if I remember correctly, we were experiencing a short lull at that time.)

Despite Alex's spectacular radar and satellite presentations, I'd say we had sustained surface winds in the low-Cat-1 range and no higher. This would correspond fairly well with the NHC's landfall intensity estimate of 90 kt, given that Guadalupe Victoria is a bit inland from the coast. (Disclaimer: I'm not professionally trained to estimate wind speeds, and also, it was very dark, so take this for what it's worth.)

The cyclone was still impressive, however. As I mentioned above, the eye was sharply defined and apparently very small, because the calm was remarkably brief, despite our being directly in the path of the eye's center.

I'll send you complete obs once I go through my footage (which is all timestamped, for accurate record-keeping). I hope it might be helpful in some way.

 

[cdcollura]

Good day all,

... This would correspond fairly well with the NHC's landfall intensity estimate of 90 kt, given that Guadalupe Victoria is a bit inland from the coast ...

This seemed about spot-on for the winds experienced at your location.

First of all, the storm was moving W at about 10 MPH and you were 30 miles inland, meaning it would take at least 3 hours for the eye to go from the coast to your location. The eyewall began crossing the coast at the 9-10 PM CDT range so the 1 AM lull makes sense.

With the 3 hour trek across land, this would probably cause a 20-30 MPH drop in the maximum sustained winds, due to drag and lack of heat transfer. This can be 105 MPH down to 75-80 MPH.

The 90% correction factor is also for marine exposure, and not systems over land. This is where a flight level (5,000 feet MSL) wind of 100 Knots can be expected as 90 Knots near the sea surface (10 m / 33 foot height where official wind measurements are made).

Over land, I have seen 50% or less. You can have 75 MPH winds at the surface 30 miles inland, but 5 or 10 thousand feet up, it can still be 120 MPH. Mountains (Cuba, D Republic) will cause even more of a difference while flat, swampy terrain (FL Everglades) can be similar to marine.

 

[Josh Morgerman]

I've been reviewing my footage this morning, which is precisely timestamped, and actually, the lull in Guadalupe Victoria lasted from about 12:25 am to 12:45 am CDT. As I mentioned above, the lull was very clean and pronounced.

Interestingly, this doesn't jibe that well with the NHC's 1 am CDT position, which is literally at Guadalupe Victoria (plug it into Google Maps to see). The center was actually past us by that time and we were getting hammered by hurricane winds on the backside around then. Given this, I'm wondering if the NHC might want to adjust the position at that time in postanalysis.

 

[cdcollura]

Good day all,

... I'm wondering if the NHC might want to adjust the position at that time in postanalysis ...

I agree, but it's only like a 25 minute "discrepancy" ... As the satellite and radar positions do indeed have some sort of latency (6 minutes for radar and 30 minutes or so for satellite).

For such international positions (Mexico in this case), I would expect some such latency / timing issues. Second, I ahve been on US chases and in the eye and NHC has the eye a half hour after that (or more).

Maybe it's just that, data LATENCY?

With supercells we see it too, we see the tornado on the ground, and no "couplet" and the tornado dissapates, then the massive couplet appear on the next scan 6-7 minutes later.

 

[rdale]

I agree, but it's only like a 25 minute "discrepancy" ... As the satellite and radar positions do indeed have some sort of latency (6 minutes for radar and 30 minutes or so for satellite).

Actually there's very little latency on radar. It's about 15-45 seconds usually from scan complete to display. Satellite takes about 10 minutes.

With supercells we see it too, we see the tornado on the ground, and no "couplet" and the tornado dissapates, then the massive couplet appear on the next scan 6-7 minutes later.

That isn't data latency at all. That means the couplet wasn't visible in radar imagery until 6-7 minutes later. There is no "delay" in radar images.

 

[Jack Beven]

I've been reviewing my footage this morning, which is precisely timestamped, and actually, the lull in Guadalupe Victoria lasted from about 12:25 am to 12:45 am CDT. As I mentioned above, the lull was very clean and pronounced.

Interestingly, this doesn't jibe that well with the NHC's 1 am CDT position, which is literally at Guadalupe Victoria (plug it into Google Maps to see). The center was actually past us by that time and we were getting hammered by hurricane winds on the backside around then. Given this, I'm wondering if the NHC might want to adjust the position at that time in postanalysis.

Josh, please send your obs along when you get the chance. My colleague Richard Pasch will be doing the post-analysis on Alex.

One comment is that if the eye passed over Victoria at about 12:30 AM, it was probably about 0.1 degrees west or west-southwest of there at 1 AM. We probably will be able to tweak the best track a tenth of a degree.

Jack Beven

 

[Josh Morgerman]

Josh, please send your obs along when you get the chance. My colleague Richard Pasch will be doing the post-analysis on Alex.

One comment is that if the eye passed over Victoria at about 12:30 AM, it was probably about 0.1 degrees west or west-southwest of there at 1 AM. We probably will be able to tweak the best track a tenth of a degree.

Jack Beven

Very cool. I'm glad the info could be useful. I'll send it along ASAP.

What was the lowest barometric pressure you recorded and at what precise time was that? Were you able to determine what elevation you were at, so you could adjust that barometric pressure accordingly?

No pressure readings, unfortunately.

 

[Joe Dorn]

Actually there's very little latency on radar. It's about 15-45 seconds usually from scan complete to display. Satellite takes about 10 minutes.

Would you please explain this statement... It is my understanding that a complete WSR-88D volume scan takes about five minutes,varies with mode, and in the fast moving systems this produces a 'graininess' that is very apparent as in crossing a coast line or IH-35 in my case

I believe there is a mode that allows new scans to replace older scans but this can cause confusion since there is a five minute difference between 'adjacent' tilts.

There is probably very little delay once a volume scan is complete to delivery time...

I would like a reference please...

 

[Jeff Snyder]

There is probably very little delay once a volume scan is complete to delivery time...

I would like a reference please...

You get radar data BEFORE the entire volume completes. In other words, you don't need to wait for the entire volume to be collected before the data get delivered to you. For example, GRx downloads data on an elevation-by-elevation basis, AFAIK. Each elevation angle only gets updated every 4.5-5.5 mins (depending upon VCP 11/12/211/212), but the data you get to see may only be as "old" as 45 seconds from the end of that elevation scan.