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Re: Max winds Irma and Maria

Posted by Chris in Tampa on 10/2/2017, 8:10 am

Based on recon, Maria's wind was worse at landfall in Puerto Rico than Irma in the Keys, both for highest wind speed at flight level and the size of the wind field. The surface winds may have been closer, but the SFMR data might not have been as good over shallower waters for Irma.

As for surge, that's a different story. The majority of the damage is likely surge in the hardest hit Keys and wind in Puerto Rico. Spending just a minute looking at Puerto Rico's coast:

You can see some areas where the water definitely rose. But most all areas are high in Puerto Rico. I only took a quick look. But even right next to the coast, you can visibly see wind damage all over the place where damage from the surge is much harder to find even among properties right on the coast. (of course fresh water flooding was a big problem for them inland)

Meanwhile in some areas of the Keys, pictures on the ground made it clear the water level came up a lot, where sometimes roofs were intact and a first floor was completely washed away. (and lots of tossed boats, as well as debris covered roads)

Recon does indicate some strong winds in parts of the Keys, but due to shallow water, some SFMR readings (10 second estimated surface winds as estimated by SFMR instrument on the aircraft) in the Keys may not be valid. I wasn't watching recon during Irma, but taking a look now I see some values that were obviously suspect. (well away from the center or over land) I remove values like that from file names in the recon system so that the values do not appear in the highest obs I have listed for each mission. There were other values that are questionable. Some might be accurate.

Looking at the Keys there seems to be quite a bit of roof damage, but the complete structural failures seem more due to surge. I can't tell from aerial pictures too much, but from the pictures on the ground it seemed to be more surge.

Irma had weakened more by the time it got to the Florida peninsula. The damage in Marco Island doesn't seem very bad at all compared to the Keys. Some roofs damaged as well as some screen enclosures over pools destroyed. That is in terms of wind. For surge, I don't see debris on roads. I don't even see much evidence in backyards of the water coming up much. In some areas you can see some evidence of where the water level was, but it might only be a few feet above the seawall, maybe less. Can't tell well by air. But I don't even see a whole lot of roof damage. I came across one that had significant damage after spending a few minutes looking at imagery.

Irma damage in Marco Island:

I don't even see boats tossed around very much. Most seem fairly okay other than the couple here I happen to come across:
They might be smaller.

Not to minimize the damage anyone got there, but compared to what this could have been, most were extremely lucky there in that area. It was significantly worse in areas of the Keys.

Irma recon (Missions 29, 30 and 31):

Maria recon (Missions 7 and 8):

Let's start with Irma.

Mission 29 was from just off coast of Cuba to a little over half way to the Keys.

Highest Flight Level Wind (30 sec. Avg.): 123 kts (141.5 mph)
Highest SFMR Peak (10s Avg.) Sfc. Wind: 111 kts (127.7 mph)

Mission 30 was from when the storm was nearly about to cross the Keys to a little over half way from making landfall on the peninsula.

Highest Flight Level Wind (30 sec. Avg.): 118 kts (135.8 mph)
Highest SFMR Peak (10s Avg.) Sfc. Wind: 110 kts (126.6 mph)

Mission 31 didn't get to sample the storm much before landfall. The highest winds here are therefore low. They actually launched a sonde over Naples. (it might have landed next to a condominium complex where it recorded 939mb and 9 knots of surface wind)

Highest Flight Level Wind (30 sec. Avg.): 92 kts (105.9 mph)
Highest SFMR Peak (10s Avg.) Sfc. Wind: 80 kts (92.1 mph)

Talking about Naples area......

Mission 31 (1 center fix over land):

While mission 31 did not get to sample the storm much at all, the storm was weakening since the Keys. The highest SFMR was about 6 to 7 nautical miles west of the center (the center was where that sonde on land landed). Center at that time was about 3 nautical miles south/SSE of the center of the city of Naples. They didn't fly in the NE quadrant and by the time they got to the SE quadrant some, it was even more over land. NHC's landfall intensity was 115mph and they said that "A 130 mph wind gust was recently reported by the Marco Island Police Department" at the time. I don't have enough information from recon.

Mission 30 (4 center fixes):

Fourth center fix:

When the storm was about 45 nautical miles south of Naples, the last pass (936mb sonde, 0 knots of surface wind) in mission 30 found 93 kt (107.0 mph) SFMR in the NW quadrant. (technically suspect, but one next to it was 90kts and seems valid)

Third center fix:

They didn't sample the NE quadrant for the last two center fixes in this mission. (second to last sonde in center: 934mb, 9 knots of surface wind)

SE quadrant: 82 kts (94.4 mph) SFMR

NW quadrant: 94 kts (108.2 mph) SFMR was suspect, but 92 kts right next to it.

We'll get to the other center fixes visually.

Talking about the Keys......

Images below are some of the SFMR values for various passes around the Keys.

The last center fix in mission 29 (where they did 5 center fixes) was where they last traveled into the NE quadrant before the Keys. The last center fix was about 35 nautical miles south center of Big Pine Key. 929mb sonde with 8 knots of surface wind. (see the northernmost 929mb icon in the image) They came in from the NE quadrant and exited in the NW heading home.

NE quadrant:

Flight Level Wind (30 sec. Avg.): 115 knots (132 mph)
Peak (10 sec. Avg.) Flight Level Wind: 120 knots (138 mph)

You can see the 119 knots (137 mph) SFMR value that was suspect.

Shortly after, center, they did a bit of a loop in it and then went into the NW quadrant.

NW quadrant:

Flight Level Wind (30 sec. Avg.): 102 knots (117.4 mph)
Peak (10 sec. Avg.) Flight Level Wind: 110 knots (126.6 mph)
SFMR Peak (10s Avg.) Sfc. Wind: Two readings of 107 knots (123.1 mph) in a row, neither suspect.

Other vortex icons in first image, beyond southern five, are from later missions.

The estimated SFMR values for Irma are more challenging due to shallow water. Using suspect values before landfall in the Keys, over deeper water, here is what the plane found, in order, traveling from NE quadrant toward center:

121mph suspect SFMR about 13 nautical miles NE of center.
Missing SFMR value.
137mph suspect SFMR about 11 nautical miles NE of center.
115mph suspect SFMR about 8 nautical miles NE of center.

The storm was about 34 nautical miles from landfall at that point.

Here is what the plane found about 8 nautical miles after landfall in the Keys, in order, traveling from NE quadrant toward center:

78mph SFMR about 18 nautical miles NE of center.
89mph suspect SFMR about 17 nautical miles NE of center.
98mph suspect SFMR about 16 nautical miles NE of center.
81mph suspect SFMR about 14 nautical miles NE of center.
119mph suspect SFMR about 13 nautical miles NE of center.
121mph SFMR about 11 nautical miles NE of center.
115mph suspect SFMR about 10 nautical miles NE of center.
62mph suspect SFMR about 8 nautical miles NE of center.

Is the 81mph too low or some of the others high? I don't know.

Now to Maria.

In Maria before landfall, 132mph SFMR about 14 nautical miles SW of center. The ob next to it, nearer to the center was 134 mph and noted as suspect. In the NE quadrant, there were two missing obs before the highest values. Right after that there was a suspect SFMR of 132 mph and one after it that was not suspect and was 128mph. 128mph value was 16 nautical miles NE of center.

That's about a 30 nautical mile wide area of 130mph winds. SFMR is only 10 second estimated surface values, but a lot of times the NHC uses it for advisories which are 1 minute sustained. Likely in case there are higher winds or because that's the best estimate they have. I also like to look for two high values right together.

For mission 8 into Maria, the storm was over land. Here are a few SFMR values from around the island. (arrows show the direction recon traveled)

Here are some key takeaways regarding flight level wind...

In the NE quadrant for Maria before landfall in Puerto Rico, 30 second flight level winds at the time were 164mph. 10 second were 168mph.

In the NE quadrant for Irma before landfall in Keys, 30 second flight level winds at the time were 132mph. 10 second were 138mph.
In the NE quadrant for Irma just after landfall in Keys, 30 second flight level winds at the time were 134mph. 10 second were 136mph.

The Keys are flat, Puerto Rico has high elevations. Puerto Rico would have received some of those higher winds. The surface wind at sea level may not seem too different based on recon between the storms, but there are more observations that support a 130mph+ intensity in Maria. (and on both sides of the storm) Just one for Irma. While both storms were weakening, Maria had more powerful flight level winds that some of the higher elevations of Puerto Rico would have felt. The wind field of strongest winds was smaller in Irma.

From sondes, there were some extremely powerful momentary winds in Maria before landfall that higher elevations would have experienced.

About 42 nautical miles SE/ESE of Puerto Rico, a sonde had momentary winds of 184 mph at the 894mb level. Winds were only 113mph 2mb above the surface level there, but it likely got tossed out from the highest winds in the eyewall. The 850mb level was 747m (2,451 ft). Surface was 925mb. So somewhere between 2,451 ft and sea level, momentary winds were 184 mph.

Later, on Vieques, a sonde landed there. It was released about 11 nautical miles E/ESE of where it landed on the island, in a lake. It had momentary surface (957mb) winds of 67mph because it too was knocked out of the eyewall. At the 886mb level the winds were 177mph. 925mb level there was 298m (978 ft) and 850mb level was 1,036m (3,399 ft). So somewhere between those altitudes were those highest winds.

That's not to say there weren't some strong winds found in Irma before/at landfall by sonde.

The southern coast of Boca Chica Key, where the Naval Air Station Key West is, had a sonde land on it. Surface winds were 105mph. Surface level was 944mb. The 921mb level had momentary winds of 158mph. 925mb level was 182m (597 ft). That sonde was launched from where I have "SFMR - 127mph - Shallow Water" in one of the images above. The sonde landed where the sonde icon is, east of Key West and SW of Big Coppitt Key label.

But given the Keys are flat, they would not have seen these higher winds unless they mixed down to the surface more. I don't know if that is the case.

But of course, Maria had a much more massive impact due to impacting more people with strong winds.

There are very few parts of Florida that experienced the winds that most of Puerto Rico experienced. Then again, more of the state probably had more significant damage due to surge than Puerto Rico. I would certainly think that, most especially considering all the flooding on the east coast of Florida in addition to the Keys and parts of SW Florida.

If a hurricane happens at night or someone hasn't been through a hurricane before, or even a tropical storm, I think it simply seems scarier. It's important those people realize they haven't been through what they probably think they have.

I try to stress that here in Tampa to the people I have talked to. I think one person described it here as kind of scary. I forget how they put it. But it just had moderate tropical storm conditions over me here. It didn't even gust over hurricane force at the airport a few miles from me. I don't know what it sounded like, but back in 2004 when I was here for moderate tropical storm conditions it did sound kind of scary with my house boarded up then and it was at night. (I know more now.) Wind howls between houses as it funnels between. A tropical storm is going to take down a lot of trees and knock out a lot of power. That just looks like a lot of damage. For the Keys, the wind likely would have done a lot of damage to homes not well built. I don't know which came first there, wind or surge. Wind could have still done a lot of damage to homes not built as well and then the surge came and masked that.

But the scale is just so much larger in Puerto Rico. I haven't really seen too much specifically about the U.S. Virgin Islands. They have not been talked about as much.


In this thread:

Max winds Irma and Maria - Stedwoo, 10/1/2017, 11:16 pm

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