ATL: NANA - Remnants - Discussion

[Ubuntwo]

53kt sustained wind at an offshore station (Carrie Bow), pressure bottomed out at 998.8. The center clearly passed to its south though.

Edit: And we have landfall - thankfully in a sparsely populated area.

[CrazyC83]

53kt sustained wind at an offshore station (Carrie Bow), pressure bottomed out at 998.8. The center clearly passed to its south though.

Edit: And we have landfall - thankfully in a sparsely populated area.

That would suggest a landfall pressure of 993 or so. I also would have only gone 60 kt at the time of the reading, but I doubt the NHC will backtrack when it is otherwise inconclusive (even though that is what I would have set it at).

If that is 10-min sustained, that would translate to 60 kt.

[CrazyC83]

How comfortable would the NHC be with a post-storm downgrade? Looking at the evidence:

* The 62 kt SFMR was likely valid. However, that would be just below hurricane force.

* The 72 kt winds at 700 were much higher than the winds at 850 at the same location. The SFMR - would be reliable as the water is very deep there - was only in the low 50s at the same time. I'd suggest that reading is probably too high.

* The surface observation at Carrie Bow Cay of 53 kt, if 10-min sustained, would translate to 59 kt. That would validate the SFMR reading.

* The pressure was likely steady state in the hours leading up to landfall. My estimate at landfall is 993 mb, based on the reading (adjusted) at Carrie Bow.

Personally, I would set the intensity - both peak and landfall - at 60 kt. However, I have a hard time imagining the NHC downgrading given the standard level of uncertainty. A post-storm downgrade is very rare.

[EquusStorm]

And here's the landfall shot.



Seemed to be ramping back up again at landfall with hot towers and lots of lightning; no doubt going to get some gusts on the coast. Of course the flood and mudslide threat is absolutely dire and that's going to be the big problem.

[Extratropical94]

Dunno if this belongs here or in the EPAC season thread, but anyways...

The remnants of Atlantic basin Hurricane Nana could emerge over the
eastern Pacific waters near the Gulf of Tehuantepec on Friday.
Unfavorable upper-level winds are expected to limit development
through the weekend while the system moves generally
west-northwestward near the southern coast of Mexico.
* Formation chance through 48 hours...low...10 percent.
* Formation chance through 5 days...low...20 percent.

[Florida1118]

Well Nana certainly doesn't look like it's going to become a hurricane!

I think you’ve batted 0/5 on cancelling storms that become hurricanes

[abajan]

If this was truly a hurricane it was for very briefly and then started weakening on approach to landfall, according to recon. It may have been but I’ve seen better cases not get an upgrade from NHC. It looked like only one or two passes supported hurricane intensity and the rest were quite below it. The area of hurricane-force winds had to have been very very small.

Very very compact indeed.

What kind of weather did you get from Nana? Seeing you're pretty far north of where the center went ashore, I'm guessing not much.

[TheStormExpert]

Well Nana certainly doesn't look like it's going to become a hurricane!

I think you’ve batted 0/5 on cancelling storms that become hurricanes

Bro, stop calling me out on comments I make! It literally just barely made it to hurricane status.

[Florida1118]

Well Nana certainly doesn't look like it's going to become a hurricane!

I think you’ve batted 0/5 on cancelling storms that become hurricanes

Bro, stop calling me out on comments I make! It literally just barely made it to hurricane status.

Quoting is a feature of the board, bro... don't make so many unsound, declaratory statements cancelling things year after year, storm after storm only to end up eating a buffet of crow, and perhaps you'll find people stop quoting you (or in your opinion, "calling you out") on on the posts you make in virtually every topic on S2k

[TheStormExpert]

I think you’ve batted 0/5 on cancelling storms that become hurricanes

Bro, stop calling me out on comments I make! It literally just barely made it to hurricane status.

Quoting is a feature of the board, bro... don't make so many unsound, declaratory statements cancelling things year after year, storm after storm only to end up eating a buffet of crow, and perhaps you'll find people stop quoting you (or in your opinion, "calling you out") on on the posts you make in virtually every topic on S2k

Well Nana didn’t look too promising earlier yesterday. Besides calling specific people out like this is not polite in my opinion.

[cheezyWXguy]

Bro, stop calling me out on comments I make! It literally just barely made it to hurricane status.

Quoting is a feature of the board, bro... don't make so many unsound, declaratory statements cancelling things year after year, storm after storm only to end up eating a buffet of crow, and perhaps you'll find people stop quoting you (or in your opinion, "calling you out") on on the posts you make in virtually every topic on S2k

Well Nana didn’t look too promising earlier yesterday. Besides calling specific people out like this is not polite in my opinion.

I think the issue is that you tend to take definitive stances on subjects that the existing data doesn’t definitively support. I will say though, I was with you on Nana not becoming a hurricane. I thought it was done after it’s center became exposed.

[wx98]

...NANA WEAKENING RAPIDLY OVER NORTHERN GUATEMALA AND SOUTHEASTERN MEXICO... ...ALL COASTAL WATCHES AND WARNINGS DISCONTINUED...
10:00 AM CDT Thu Sep 3
Location: 16.4°N 90.3°W
Moving: W at 15 mph
Min pressure: 1004 mb
Max sustained: 45 mph

[MarioProtVI]

Wonder if Nana might hold on long enough to cross over to the EPac intact - that would be very 2020 indeed.

[ClarCari]

Wonder if Nana might hold on long enough to cross over to the EPac intact - that would be very 2020 indeed.

And in very 2020 fashion for the EPAC, it will fizzle the moment it touches that water

[SconnieCane]

Wonder if Nana might hold on long enough to cross over to the EPac intact - that would be very 2020 indeed.

And in very 2020 fashion for the EPAC, it will fizzle the moment it touches that water

Yep. NHC not anticipating Pacific redevelopment from ex-Nana.

[TheStormExpert]

Quoting is a feature of the board, bro... don't make so many unsound, declaratory statements cancelling things year after year, storm after storm only to end up eating a buffet of crow, and perhaps you'll find people stop quoting you (or in your opinion, "calling you out") on on the posts you make in virtually every topic on S2k

Well Nana didn’t look too promising earlier yesterday. Besides calling specific people out like this is not polite in my opinion.

I think the issue is that you tend to take definitive stances on subjects that the existing data doesn’t definitively support. I will say though, I was with you on Nana not becoming a hurricane. I thought it was done after it’s center became exposed.

Same here. Once I saw the center being on the northern edge of the convection due to the relentless northerly shear I had doubts.

[EquusStorm]

Nana is booking it across Guatemala. Got some mountains incoming but if that were flat land I'd say the center would survive to the EPac. If it were a much stronger system like the many majors that have crossed here, maybe, but oughta lose the LLC over those mountains.

[Buck]

...NANA WEAKENS TO A TROPICAL DEPRESSION...
4:00 PM CDT Thu Sep 3
Location: 16.0°N 91.1°W
Moving: WSW at 14 mph
Min pressure: 1006 mb
Max sustained: 35 mph

[us89]

Welp, looks like the mountains of Guatemala were too much for the LLC.

...NANA DISSIPATES NEAR THE GUATEMALA/MEXICO BORDER...
...THIS IS THE LAST ADVISORY...


SUMMARY OF 1000 PM CDT...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...15.6N 92.0W
ABOUT 120 MI...195 KM NW OF GUATEMALA CITY GUATEMALA
MAXIMUM SUSTAINED WINDS...30 MPH...45 KM/H
PRESENT MOVEMENT...WSW OR 250 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...1007 MB...29.74 INCHES

[Shell Mound]

How comfortable would the NHC be with a post-storm downgrade? Looking at the evidence:

* The 62 kt SFMR was likely valid. However, that would be just below hurricane force.

* The 72 kt winds at 700 were much higher than the winds at 850 at the same location. The SFMR - would be reliable as the water is very deep there - was only in the low 50s at the same time. I'd suggest that reading is probably too high.

* The surface observation at Carrie Bow Cay of 53 kt, if 10-min sustained, would translate to 59 kt. That would validate the SFMR reading.

* The pressure was likely steady state in the hours leading up to landfall. My estimate at landfall is 993 mb, based on the reading (adjusted) at Carrie Bow.

Personally, I would set the intensity - both peak and landfall - at 60 kt. However, I have a hard time imagining the NHC downgrading given the standard level of uncertainty. A post-storm downgrade is very rare.

According to the NHC, the observation at Carrie Bow Cay was a one-minute sustained wind at 10 m. If I recall correctly, until recently the NHC would have classified a storm on the basis of contextual information, e.g., whether flight-level (700-mb) winds correlated closely with winds observed just below that level and/or nearby, taking into account SFMR biases, sondes, radar data (whether the winds were contaminated by rainfall, were in rain-free areas, matched ASCAT and surface data in situ, including ship, land, and buoy, taking into account density of coverage...), et al. as well. Now the NHC seems to be basing estimates of surface winds on the averaged peak 10-s observations from reconnaissance-based FL and SFMR data, without really taking into account other factors such as pressure trends, convective and/or structural organisation, surface vs. aircraft observations, discrepancies between FL and lower-level and/or SFMR-derived winds, etc. Five or ten years ago the NHC likely would have looked at the data you mentioned, taken into account context, and went with estimated peak winds of 55 (maybe 60) knots instead of 65 knots. Furthermore, reports from the area of landfall in Belize showed only minor roof damage to a relative handful of structures in Dangriga, Silk Grass, and Hopkins. A strong but compact tropical storm could easily cause similar damage, given the comparatively poor standards of construction in rural Belize vs., say, Bermuda or the Bahamas. Personally, I think this was likely 55 knots/993–5 mb around the time of landfall in Belize, since Carrie Bow Cay likely experienced the RMW and experienced the strongest convection on the NNW side of a WSW-moving TC. I normally don’t disagree with the NHC, but I am puzzled as to why this was considered a Cat-1.