SPAC: HAROLD - Post-Tropical

[doomhaMwx]

Leaving Vanuatu now.

[aspen]

Harold is recovering...AGAIN?!

I expected that landfall to disrupt its core for the final time. Now it’s almost a Cat 5. However, the eye seems to be filling up a bit, so I’m going to assume this latest burst of intensification is just about over.

[Nancy Smar]

25P HAROLD 200406 1200 16.0S 168.8E SHEM 145 912

[Nancy Smar]

At 11:00pm local time, Severe Tropical Cyclone HAROLD [898hPa] Category 5, was
located at 16.0 degrees South 168.8 degrees East. This is about 80KM east northeast
of Ambrym and 105KM northeast of Epi. The system is positioned at the bottom right
corner of square letter H, number 5 (H,5) of the Vanuatu Tropical Cyclone Tracking Map.
Severe Tropical Cyclone HAROLD has been moving in an east southeasterly direction at
19KM/HR (10Knots) in the past 3 hours.
Maximum sustained winds close to the center are estimated at 230KM/HR (125Knots).
Severe Tropical Cyclone HAROLD is forecast to be at 16.7 degrees South
171.1 degrees East in the next 24 to 48 hours.

[aspen]

Could Harold have reached 155 kt at around 09z?

[1900hurricane]

This is one ugly 145 kt TC. Might be starting eyewall replacement because it sure got frumpy.

[aspen]

This is one ugly 145 kt TC. Might be starting eyewall replacement because it sure got frumpy.

Looks like one to me. Imagine if Harold somehow recovers from this as well. It’s been awfully persistent these last few days.

[Nancy Smar]

CIMSS/NESDIS-USAF/NRL AMSU TC Intensity Estimation:
TROPICAL CYCLONE 25P
Sunday 05apr20 Time: 2237 UTC
Latitude: -15.71 Longitude: 166.66
Storm position corresponds to AMSU-A FOV 4 [1<--->30]
-----------------------------------------------------------------
| Estimated MSLP: 909 hPa
| Estimated Maximum Sustained Wind: 168 kts
| Estimate Confidence: Fair ( +/- 15mb +/- 20kts )
-----------------------------------------------------------------
Storm is sub-sampled: Bias correction applied is -25.0 hPa
Channel 8 (~150 hPa) Tb Anomaly: 3.10
Channel 7 (~250 hPa) Tb Anomaly: 1.54
RMW: 14 km
RMW Source is: MW
Environmental Pressure: 1006 (JTWC)
Satellite: NOAA-MB
ATCF data for Month: 04 Day: 06 Time (UTC): 1200

[1900hurricane]

What in the world, what kind of outlier pass is that??? That was when it was first making landfall too.



As for the apparent recent weakening trend, I wonder if it's in fact a dry air intrusion. WV and airmass loops indicate a region of subsidence on the system's back side, and as it rapidly intensified, requiring it to draw in more air, wrapped some of that air in and ingested it. Could be a reasonable explanation based on recent microwave imagery.

[Astromanía]

Just wow!

[Astromanía]

Why they used very similar names this season on SWIO and SPO basins? Herold vs Harold, what the heck I thought they should prevent this to happen un the same season in order to avoid confusions. Why we don't have Hirold on Australian basin this season then? lol

[Chris90]

Why they used very similar names this season on SWIO and SPO basins? Herold vs Harold, what the heck I thought they should prevent this to happen un the same season in order to avoid confusions. Why we don't have Hirold on Australian basin this season then? lol

There's more than one agency in the S. Hemisphere that monitors the tropics. There are several RSMCs, and they each have their own name lists that they use, and they don't have to match their name list up with the name list of another RSMC.

In the N. Hemisphere the name Maria is on the typhoon list, despite the fact that it was also used in the Atlantic until 2017. It was even used in the WPac after ATL Maria '17 occurred.

The only agency that ends up using the same name or different spelling of the same name is the JTWC, and they're not a RSMC for any basin.

[Yellow Evan]

This would've been a raw beyond 7.5 (7.7) if this was in the WPAC

2020APR06 071000 6.9 922.6 137.4 6.9 7.4 7.4 NO LIMIT OFF OFF OFF OFF 10.92 -81.66 EYE 17 IR 59.7 -15.82 -168.05 ARCHER HIM-8 36.4

ADT is more conservative in the SHEM compared to the WPAC as well? I thought it was only more conservative in the NOAA basins compared to the rest of the world due to differences in the tropopause? Is the SHEM troposphere that much colder than the WPAC?

[1900hurricane]

Looks like it was indeed dry air that knocked Harold down a peg, but at a higher layer than I'd usually look for. When dry air typically interrupts a tropical cyclone, it fairly low level and in the TC's natural inflow. This makes it easy to pick out on PW and even microwave images. However, there was no real distinct dry air telltale on either of these types of imagery (PW image below). However, you could see a dry region hanging around the upshear anvil on water vapor imagery, particularly on Himawari-8 band 8 (which I previously posted above). Band 8 is upper level water vapor, so the dry air might be related to subsidence as upshear air aloft encounters Harold's outflow and "piles up." The dry air appeared to be sneaking beneath the outflow a bit, so perhaps the shear layer was deep enough to where the lower part of the layer was able to progress unhindered towards the central vortex, bringing the subsident dry air aloft with it and introducing it to the core. GFS analysis seems to indicate this was the case, as there is a sudden jump in winds and drop in RH around the 300-400 mb layer (also below). Therefore, this dry air/mid shear combo is most likely the responsible culprit for the sudden weakening of TC Harold today.

[aspen]

The "H" in "Harold" stands for "Hideous" right now:

[1900hurricane]

SAR got Harold at 0714Z.



I was trying to pull values from the text file for the pass on NRL, but the islands are making it difficult.

[1900hurricane]

This thing is legit Parma collapsing right now.

[aspen]

That is the ugliest 135 kt system I have ever seen. That’s a 115 kt low-end Cat 4 at the absolute highest; it not even be a major hurricane anymore.

[TheAustinMan]

SAR got Harold at 0714Z.
[...]

Definitely a very intriguing addition to the tropical cyclone intensity estimation arsenal. Some pretty high-intensity data came out of that, and it's pretty neat that we're able to get such high resolution through all the cloud cover, rain, and turbulence within the cyclone. The synthetic radar yielded a peak wind of 150 kt in the storm's northeastern quadrant (in line with traditional models of the left-front quadrant in the SHEM) and a radius of maximum wind of 7 nautical miles (which is quite tiny!). Sampled winds from the radar were 116kt in the two hind quadrants and 126kt in the right front quadrant. Also, lots of fantastic data on the site I linked below. Definitely recommend for all you data junkies.

759 KB. Source: https://www.star.nesdis.noaa.gov/socd/mecb/sar/AKDEMO_products/APL_winds/tropical/?year=2020&storm=SP252020_HAROLD


351kB. Same source.

[cycloneye]

25P HAROLD 200407 0000 16.7S 171.2E SHEM 115 942