Topic: Tropical Cyclone Guba - Coral Sea: 13 - 19 Nov 2007

[Mike]

Development is good for this system to intensify over the coming days to TC status.  Text herein from JTWC at https://metocph.nmci.navy.mil/jtwc/warnings/sh9608web. txt and imagery.  Certainly showing nice circulation and once he/she steers clear of land and into the Coral Sea it will gather momentum.  one to watch as La Nina shows us early signs of things to come.

Mike


WTPS21 PGTW 130200
MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
160 NM EITHER SIDE OF A LINE FROM 9.7S 150.9E TO 12.7S 147.4E
WITHIN THE NEXT 12 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY
ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME.
WINDS IN THE AREA ARE ESTIMATED TO BE 25 TO 30 KNOTS. METSAT IM-
AGERY AT 130100Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 10.6S 150.2E. THE SYSTEM IS MOVING SOUTHWESTWARD AT 11
KNOTS.
2. REMARKS: THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 7.9S
152.4E, HAS BEEN RELOCATED NEAR 10.6S 150.2E, APPROXIMATELY 460
NM NORTHEAST OF CAIRNS, AUSTRALIA. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY INDICATES THAT THE LOW-LEVEL CIRCULATION CENTER (LLCC) HAS
CONSOLIDATED AND BECOME BETTER DEFINED OVER THE PAST 06 TO 12 HOURS.
RECENT MICROWAVE IMAGERY AT 121955Z (WINDSAT 37H) AND 121521Z (AMSR
-E) INDICATE THAT THE LLCC HAS CONSOLIDATED AND TRACKED ACROSS
THE SOUTHEASTERN TIP OF PAPUA NEW GUINEA, UNFORTUNATELY, SURFACE
OBSERVATIONS ARE SPARSE. HOWEVER, A SHIP REPORT FROM THE CAPE
DENISON (10.0S 152.9E, APPROXIMATELY 170NM EAST OF THE LLCC) SHOWS
NORTHEASTERLY WINDS AT 19 KNOTS AND SLP NEAR 1007MB. THE UPPER-
LEVEL ENVIRONMENT REMAINS FAVORABLE FOR DEVELOPMENT WITH GOOD
POLEWARD AND EQUATORWARD OUTFLOW AS WELL AS WEAK VERTICAL WIND
SHEAR. LAND IS CURRENTLY HINDERING SIGNIFICANT DEVELOPMENT AND
WILL CONTINUE TO SLOW DEVELOPMENT FOR THE NEXT 06-12 HOURS.
THEREFORE, THE DISTURBANCE IS FORECAST TO IMPROVE SIGNIFICANTLY
AS IT TRACKS INTO THE CORAL SEA. MAXIMUM SUSTAINED WINDS ARE
ESTIMATED AT 25 TO 30 KNOTS. MINIMUM SEA LEVEL PRESSURE IS
ESTIMATED TO BE NEAR 1002 MB. THE POTENTIAL FOR THE DEVELOPMENT
OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS
NOW GOOD.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED
BY 140200Z.//
NNNN

[Mike]

Indeed.  I've been watching the storms increase for the last week or two in the region, just so much activity coming and going but the wind streams were flowing right into that spot.  I had not viewed the tropical charts for about two days and only noticed it on the BoM satpic at the size of the circulation area.

JTWC obviously are noting its prowess thus far and likelihood of getting even more organised.  A nice start to the season one would think!

[mitch]

The bureau don't seem to be that interested, only giving it a medium potential to develop into a tropical cyclone. Are cyclones this early in the season common? I've read that there is a la nina occurring but then I've read that the sea temperature north of Australia is not what is expected of la nina conditions, apparently cooler than usual, but I don't see that.

[Mike]

La Ninya effect definitely on the cards.  Most weather websites have indicated this and even BoM have strongly suggested it's here or close to it.  Most of the models along the northern Australian coastline have shown regular and sustained influences for La Nina.  I guess QLD BoM are jsut seeing what form it takes over the next 24-36 hours, but from the structure of it's circulation it has got some good potential once out in the open water. Increasing thunderstorm activity around and within it will help it so long as the weather conditions it enters is not hostile, no showing hostility just yet!  SST's along the northern parts of Oz have dramatically increased - probably a strong word - but they are well into what you would expect for this cycle of weather expected.  I've seen a gradual increase over the months of sea temps especially.

Mike

[Carlos E]

Well this is an interesting start to the Cyclone Season. I didn't think it would be this early (if).

I think that one will intensify into a Cyclone before midnight tonight. There's another minor one in the Indian.

Does anyone know the earliest a Cyclone has formed in Brisbane's area?

[Michael Bath]

Have a look through this list of BoM tracked tropical cyclones:

http://australiasevereweather.com/cyclones/bomsumm.htm

[Steven]

I've noticed the Bureau have predicted the low to intensify and move westwards until it supposed to weaken sometime Wednesday or Thurdsay, I don't know what anyone else thinks, but that sounds like wishful thinking upon the Bureaus behalf. Only now I think the Bureau are paying more attention to this system, though its interesting what this low does.

[Mike]

'experts' up here say we'll get an early cyclone possibly in November - suppose there's a miracle chance that if it continues west, holds its structure, meets warm waters over the Cape and wanders off into the Gulf of Carp that it might do something - wishful thinking on my part, but stranger things have happened haven't they!

Mike

[Carlos E]

After Monica and Ingrid I wouldn't rule that one out.

Meh. I wish the satellites updated more. >_>

[Carlos E]

Ugh.

Guba is an incredibly difficult storm to predict. It's very small as well (which is strange considering how big it looked as a Tropical Low).

[Carlos E]

Cyclone Warning for Queensland now. Guba decided to finally speed up.

[Mike]

BoM regularly refer to this sized cyclone as a 'Midget cyclone' due to it's small size and inconsistent structure.  Tracey was a midget and although small, she was compact and strong.  BoM here don't expect anything from this one, they're going for a coastal crossing as a Cat1 or tropical low.  Seems there's just an unfavorable area to which to strengthen for this one....

Mike

[orage]

Hi all

Can anyone tell me what the reason is for the storm's eratic movement?

It is certainly exciting watching it, being the first one of the season. I don't know that I will get any good radar images on landfall though. Not like the images of TC george last year anyway.

[Carlos E]

George's, Larry's and Monica's images on the radar were great, this one is a total mess though on the satellite.

[Mike]

Ah that's pretty easy!  Cyclones in our region are the most erratic moving storm systems in the world.  You can see from track maps of hurricanes in the US that they follow a smooth path generally and turn in long curves.

 Ours on the otherhand are influenced by a number of variables such as trade winds, monsoonal flow, troughs, wind speeds around and in the cyclone itself.  Due to their deceleration and rapid acceleration at any given time they can either speed up and move or remain stationary for days at a time.  Influences such as the general NE/E to W/NW flow across the top of Australia results in the storms meeting just about every wind anomaly you can think of.  They swirl, wobble, bobble, double-back, stall - it's almost as if unless they are mature enough to sustain and go with the dominating flow without being influenced negatively they usually do track 'straight' once they get organised.

I have noticed that when they are imbedded in trough lines they go with the wobble of the trough over time - if you animate the MSLP maps when there is a low imbedded in it you can see how it reacts to the wobble, the cyclone will pull and drag that part of the trough with it in all manner of directions until the steering winds take hold and stablise it's track.

The speed of inflowing directional winds from the rainbands affects the storms ability to 'hold firm' and just take what is available by the scruff of the neck.  It does not take much for cyclones to strengthen or weaken as we have seen with Guba, there are so many things that influence these storms that the bureau has a hard enough time predicting their movements - even with computers!

Monica last year tracked a NW/W wobble from QLD and once in the Gulf of Carpentaria stalled - gained strength did a u-turn back towards the Cape and overnight did another U-turn back toward NT.  She was big enough to keep tracking a 'wave' track of W/NW continuously until about 400km from darwin where she took a steep SW track - we still don't know why she held her cat4 rating when half of her was over land and still had an eye which showed strong storm depth within her centre.

So if you look at all the possibilities that could affect a cyclone in our region, then double the scenarios which they can encounter, then you have your answer!

Mike