Tropical Cyclones Vivienne & Ex-Harvey

[senorpepr]

JTWC has the storm at sustained winds of 50 knots.

If the highest gusts are around 220 km/h, that equals around 137 mph.

50 knots = 58 mph

A storm with sustained winds of 58 mph producing 137 mph gusts does not seem right. Especially with a pressure of 965 mb.

According to the Dvorak scale, a Pacific cyclone with a pressure of 965 mb should be about Category 1-2 on the SS scale.

Is JTWC underestimating Harvey or am I missing something here?

I thought gusts were around 40% stronger than sustained winds for these sort of systems? Those do seem very high gusts given the sustained winds given by the JTWC.

Well... here's another thing to remember. The 58 mph from JTWC is a one-minute average. The 137 mph from BoM is a ten-minute average.

Gusts, like you said, are figured 40% than the sustained speed. Therefore BoM is observing 82 mph. However, multiply that by 1.14 to convert from 10-min to 1-min and you'll get 94 mph.

Regardless, there's still a large difference between JTWC's 50 mph and Harvey's 95 mph, but in my opinion it boils down to JTWC underestimated Harvey due to his size.

[HurricaneBill]

I guess we'll just have to wait and see if any wind reports were taken at landfall. Unfortunately, Harvey hit a largely unpopulated area of the coast.

Well, I mean unfortunate in regards to collecting data.

Although I thought I read in a news report earlier today that gusts of 200 km/h were recorded.

[HURAKAN]

Name: Ex Harvey
Severity Category: [No value set for Category]
Situation At: 4AM CST Tuesday 8 February 2005
Warning Area: Port McArthur to Mornington East
Location: 17.0S 136.9E
Recent Movement: SW at 10 km/h
Remarks: The CYCLONE WARNING for coastal and island communities between MORNINGTON ISLAND in Queensland and PORT MCARTHUR in the Northern Territory and extending about 200 kilometres inland, including BORROLOOLA, WOLLOGORANG and ROBINSON RIVER has been cancelled.

HEAVY RAIN is likely to cause WIDESPREAD FLOODING of low-lying areas in the
Roper-McArthur district today.

Well, after intensifying until the end, finally Harvey is now dissipating over western Queensland but the controversy will continue in determining how strong was Harvey at the moment it made landfall. I go with BoM.



TROPICAL CYCLONE INFORMATION BULLETIN
Issued at 12:20 pm WST on Tuesday, 8 February 2005
BY THE BUREAU OF METEOROLOGY
TROPICAL CYCLONE WARNING CENTRE PERTH

Tropical cyclone Vivienne [Severity Category 1, minimum pressure 990 hPa] was
located at noon WST near 15.8S 116.0E, that is 545 kilometres north of Dampier
and near stationary.

The cyclone is not expected to affect the WA coast within the next 48 hours.

The next advice will be issued at 7pm WST Tuesday 08 February.

Now that Harvey and Meena are out of the picture, Vivienne comes to take over the attention even though it's not to be worried about except if you are mariner, you may find chopper seas around the system. It seems like BoM doesn't have much to say about the system as you can see in their summary.

[P.K.]

Well... here's another thing to remember. The 58 mph from JTWC is a one-minute average. The 137 mph from BoM is a ten-minute average.

Gusts, like you said, are figured 40% than the sustained speed. Therefore BoM is observing 82 mph. However, multiply that by 1.14 to convert from 10-min to 1-min and you'll get 94 mph.

Regardless, there's still a large difference between JTWC's 50 mph and Harvey's 95 mph, but in my opinion it boils down to JTWC underestimated Harvey due to his size.

Surely the gusts are 40% added on to the sustained winds rather than the sustained winds being 60% of the gusts.?

I make the sustained wind speed to be 97mph, which converts to 112mph in 1 minute averages.

(Or I've gone wrong in my maths somewhere)

[HURAKAN]

BUREAU OF METEOROLOGY
WESTERN AUSTRALIA REGIONAL OFFICE

TROPICAL CYCLONE INFORMATION BULLETIN
Issued at 12:25 am WST on Wednesday, 9 February 2005
BY THE BUREAU OF METEOROLOGY
TROPICAL CYCLONE WARNING CENTRE PERTH

Tropical cyclone Vivienne [Severity Category 1, minimum pressure 990 hPa] was
located at midnight WST near 15.7S 115.9E, that is 570 kilometres north of
Karratha and is nearly stationary.

The cyclone is not expected to affect the WA coast within the next 48 hours.





For the JTWC, Vivienne heart has stopped so it's not worthy to continue issuing advisories, and according to the images, I believe they are right. But for BoM, the official agency in that part of the world, Vivienne's heart is weak but is still pumping. As you can see in the picture, Vivienne looks more like "the phantom of the opera" than a tropical cyclone!

[HURAKAN]

Bye, Bye, Short-lived Vivienne!

[senorpepr]

BoM pulled the life-support plug too...

CENTRE PERTH AT 2233UTC 8 FEBRUARY 2005
CANCELLATION OF
GALE WARNING FOR THE WESTERN AREA

Please be aware, wind gusts can be a further 40 percent stronger than the
averages given here, and maximum waves may be up to twice the height.

SITUATION
Ex-Tropical Cyclone Vivienne with central pressure 995hPa located at 2200UTC
within 30 nautical miles of
Latitude fifteen decimal five south [15.5S]
Longitude one hundred and sixteen decimal eight east [116.8E]
and recently moving east southeast at 3 knots.

AREA AFFECTED
No gales with this system.

FORECAST
Winds 20/30 knots with moderate to rough seas and low to moderate swell easing
gradually. This system has weakened over the last 12 hours, it will be
monitored for redevelopment although it is not expected to redevelop in the
short term.

At 1000UTC 09 February 15.6 south 117.0 east 995hPa
At 2200UTC 09 February 15.7 south 117.1 east 998hPa

No further warnings will be issued for this system unless redevelopment occurs.

WEATHER PERTH

[HurricaneBill]

Didn't they say Harvey was rapidly intensifying prior to landfall?

Maybe that, along with his small size, is why the intensity seemed lower than it should have been.