EPAC: HILDA- Post-Tropical

[Kingarabian]

Shear almost looks non evident right now.

[Yellow Evan]

Shear almost looks non evident right now.

Def looks nice. 95 knts may be too high,but this is a solid 80-85 knts IMO.

[Kingarabian]

Shear almost looks non evident right now.

Def looks nice. 95 knts may be too high,but this is a solid 80-85 knts IMO.

As long as it continues to be respectable by the time Recon goes in.

[Kingarabian]

TXPN24 KNES 100005
TCSCNP

A. 10E (HILDA)

B. 09/2330Z

C. 15.1N

D. 147.9W

E. ONE/GOES-W

F. T4.5/4.5/W1.0/24HRS

G. IR/EIR/VIS

H. REMARKS...SYSTEM IS TRYING TO REFORM AN EYE AND NOT WELL SEEN IN VIS
IMAGERY. MET=4.5 AND PAT=4.5 DT=4.5 BASED ON CENTER EITHER EMBEDDED IN
BLACK OR RAGGED BLACK EYE EMBEDDED IN BLACK WITH RING OF WHITE. FT IS
BASED ON DT.

I. ADDL POSITIONS

NIL


...SWANSON

[Kingarabian]

I agree.

Also looks like convection is increasing and expanding after it shrunk last night.

[srainhoutx]

At least a CAT 2 at recon was the request I heard. Good training for the 53rd crew that may not have experienced a micro 'cane'.

[Kingarabian]

At least a CAT 2 at recon was the request I heard. Good training for the 53rd crew that may not have experienced a micro 'cane'.

Haha.

Thanks for contributing and providing BTS coverage.
It's nice to know that the hurricane hunters look forward to sampling strong storms .

Are you in the AF as well?

Edit: Eye is warming!

[Yellow Evan]

Yea, I'm glad tonights recon will find a formidable hurricane and not a sheared mess.

[cycloneye]

HURRICANE HILDA DISCUSSION NUMBER 17
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP102015
500 PM HST SUN AUG 09 2015

SATELLITE FIXES FROM HFO...SAB AND REMAIN VERY CLOSE FOR LOCATION
AND PRETTY CLOSE FOR INTENSITY FOR HURRICANE HILDA. HFO AND JTWC
HAD CURRENT INTENSITIES OF 5.0...WHILE SAB HAD A 4.5. HAVE SET THE
INITIAL INTENSITY AT 85 KT. THE SATELLITE SIGNATURE OF THE
HURRICANE HAS CONTINUED TO WEAKEN. THE SYSTEM HAS BECOME LESS
SYMMETRICAL AND THE EYE IS BARELY DISCERNIBLE. HILDA IS EXPECTED
TO CONTINUE SLOWLY WEAKENING DUE TO WEAK SOUTHWEST VERTICAL
WIND SHEAR AND DECREASING SEA SURFACE TEMPERATURES.

HILDA IS MOVING TOWARD THE NORTHWEST...WITH AN INITIAL MOTION OF
305/07 KT. THE HURRICANE IS BEING STEERED BY A RIDGE ALOFT
EXTENDING WEST FROM AN ANTICYCLONE ALOFT FAR TO THE NORTHEAST.
HILDA HAS STARTED TO TURN TOWARD THE NORTHWEST AROUND THE END OF THE
RIDGE. HILDA IS EXPECTED TO START MOVING MORE SLOWLY AS THE STEERING
FLOW WILL BE QUITE WEAK.

THE TRACK AND INTENSITY FORECASTS FOR HILDA CANNOT BE CONSIDERED
SEPARATELY. IF HILDA WERE TO REMAIN A STRONG AND DEEP SYSTEM...ITS
TRACK WOULD LIKELY TO BE INFLUENCED BY STEERING FLOW THROUGH A
DEEPER LAYER OF THE ATMOSPHERE. THAT WOULD MEAN A MORE NORTHERLY
TRACK. THE WEAKER AND SHALLOWER HILDA BECOMES...THE MORE ITS TRACK
WILL BE INFLUENCED BY THE TRADE-WIND FLOW IN THE LOWER PART OF THE
ATMOSPHERE. THAT WOULD GIVE HILDA A MORE WESTERLY TRACK.

THE MODELS ARE SHOWING GOOD AGREEMENT ON AN ACCELERATING WEAKENING
TREND AS HILDA ENCOUNTERS SOUTHWEST SHEAR NEAR 35 KT DUE TO A
SUBTROPICAL JET STREAM SOUTH OF A TROPICAL UPPER TROPOSPHERIC
TROUGH OR TUTT. THE MODELS REMAIN IN GOOD AGREEMENT ON HILDA
TAKING A MORE WESTERLY TRACK AS IT WEAKENS. I HAVE SHIFTED THE
TRACK A BIT FURTHER TO THE LEFT AGAIN...CLOSE TO THE MODEL
CONSENSUS...WHILE CONTINUING A STEADY WEAKENING. THIS IS CLOSE TO
THE INTENSITY CONSENSUS AND TAKES HILDA DOWN TO TROPICAL STORM
STRENGTH IN 48 HOURS.

U.S AIR FORCE HURRICANE HUNTERS HAVE TAKEN OFF TO BEGIN FLYING
MISSIONS INTO HILDA THIS EVENING. THE DATA FROM THESE MISSIONS
SHOULD HELP REFINE OUR FUTURE FORECASTS.



FORECAST POSITIONS AND MAX WINDS

INIT 10/0300Z 15.3N 148.2W 85 KT 100 MPH
12H 10/1200Z 15.9N 149.2W 80 KT 90 MPH
24H 11/0000Z 16.8N 150.3W 75 KT 85 MPH
36H 11/1200Z 17.4N 150.8W 65 KT 75 MPH
48H 12/0000Z 18.0N 151.4W 55 KT 65 MPH
72H 13/0000Z 18.6N 152.3W 35 KT 40 MPH
96H 14/0000Z 19.0N 154.0W 30 KT 35 MPH
120H 15/0000Z 19.3N 157.1W 25 KT 30 MPH

$$
FORECASTER DONALDSON

[Yellow Evan]

Might be stronger than the CPHC said. Based on Recon, I like 95/967.

[Yellow Evan]

Very hard to estimate intensity you guys are lucky with recon going in. As you say small wind field but potent none the less i have have seen the damage small cyclones can do first hand on a weak structures never underestimate these type of systems if they landfall.

That is true. Hurricanes Iris and Felix in the 2000s in the Atlantic are excellent examples of this where Dvorak underestimated them and Recon found winds of Category 4 and 5 intensity respectively.

[Chris_in_Tampa]

Rain will of course be a threat, but it is also important to note that these are some rather elevated areas it is forecast to impact. A sonde measured winds 20 mph higher just 9 millibars above the surface. (119mph gust compared to 99mph gust at the surface) That might be around several hundred feet from the surface. This could still bring down a lot of trees due to rain and winds even as a weak tropical storm or depression, especially at higher elevations.

[Kingarabian]

Cphc needs to do a special advisory to update the intensity like how the NHC usually does it.

Not wait until the next advisory and say it's so and so knots now since it probably weakened.

[Chris_in_Tampa]

It depends what this pass has. For the first pass I would say around 85 to 90 knots, with about 973mb pressure. The sonde had 86 knots and landed in some of the most intense convection. SFMR ten second estimate was 90 knots. The sonde probably missed the absolute highest winds, though the sonde is a momentary gust it records. Maybe a half second long. (not totally sure, maybe 1 second) But the SFMR for example is something they go with a lot. (NHC at least) This is such a small storm, you could assume the highest winds were missed. Next pass is important.

[Yellow Evan]

Eh, I like 90 here. Looks it didn't miss the deepest convection by that much. We'll see what next pass has though.

[Kingarabian]

New burst of near -80c convection.

Did the CPHC have the center right?

[Yellow Evan]

Based on next pass, I like 90/971.

[Chris_in_Tampa]

I think the center, based on looking at it on satellite, is a little better organized than it was. I was thinking the pressure might have dropped some this pass, but it didn't.

[Chris_in_Tampa]

I'll add this here to:

Looks like surface wind is a significant variable in recon readings.

Can someone explain how it works?

From the plane they estimate it with the SFMR instrument. It takes a 10 second estimate.

http://www.403wg.afrc.af.mil/library/fa ... sp?id=8314
http://www.aoml.noaa.gov/hrd/project2005/sfmr.html

It's not really measured I would say like that AF article says. I would consider a sonde a measurement and the SFMR an estimate. Heavy rain, which is also estimated, could also impact the wind reading.

Highest surface wind should be near the center of the storm. If it is way out in the bands, then it is probably not representative in a tropical system. (such as it measured a gust in a thunderstorm out in the outer bands)

A sonde is a momentary gust. The sonde is falling in the atmosphere, with a little parachute.

http://www.aoc.noaa.gov/instrumentation.htm
https://www.eol.ucar.edu/isf/facilities/dropsonde/
http://scied.ucar.edu/dropsonde-animation-noaa

So the wind speed it measures is very brief since it can't stay at a level, it is always falling. I think it is about 0.5 seconds for current sondes, but I'm not really sure. Looking at the very raw sonde data, which usually seems to be every half a second, I think it means that is likely how long the reading is. However, the data as it comes across in a message like the UZPN13 one's above, have come through a program called ASPEN which may average the half second data out over a longer period near the level it says. I just don't know.

And keep in mind that advisory data from the NHC and CPHC is for 1 minute sustained surface wind at sea level. (or maybe it is 10 meters above sea level) The gusts will be higher, and those are in the forecast advisory.

For example, at 5pm HST the forecast advisory had "MAX SUSTAINED WINDS 85 KT WITH GUSTS TO 105 KT."

So we are seeing higher wind gusts than the sustained figure from the dropsonde and a bit higher from the SFMR instrument. But, are they actually perhaps sustained at some of those higher readings, or are they just sampling some of the higher gusts they know are out there? (I don't know.) In such a small storm, it might be very easy for the aircraft to miss some of the higher winds.

Higher elevations will have higher sustained winds, but that is not contained in what you see in the forecast. They might mention it elsewhere, like the discussion for example. So the mountains on the big island could see some strong winds, especially gusts.

[Kingarabian]

00z Euro shifts east.