Jeff Callaghan
To: tropical-storms@tstorms.org
Subject: [Tropical-storms] Equatorial disturbance

Satellite imagery indicates that a trough extending equatorward from a
massive Tasman Sea low appears to be associated with the development of a
disturbance near 5S 160E (SE of Chataan).
Last nights EC analysed a 850hPa cyclonic vortex at 4S 160E and it
forecasts it to move towards the equator with the winds initially
increasing in speed in the western quadrants.  By 12Z 2nd the vortex is
straddling the equator.
Nogaps at 12Z 2nd has a semicircular band of convection also straddling the
equator.
It will be interesting to watch how the equator affects this system
Jeff

Jeff Callaghan

Date: Wed, 03 Jul 2002 09:17:45 +1000
From: Jeff Callaghan <j.callaghan@bom.gov.au>
To: tropical-storms@tstorms.org
Subject: [Tropical-storms] Equatorial disturbance

Latest Quikscat (around 1920 UTC)shows centre now near 2.5S 164E with gales
near convection well away to the SW.
Latest IR shows convection since then developing around and closer to the
centre.
Jeff

Julian Heming

Jeff,

The Met Office model shows some modest development of this system and
movement towards the WSW making landfall over eastern PNG at around 07/00Z.
Do other models show any development? Six months on, maybe this will be a
southern hemisphere equivalent of the low latitude Typhoon Vamei?

Julian

---
Julian Heming  NMC Support & Tropical Cyclone Forecasting
Met Office  London Road  Bracknell  Berkshire  RG12 2SZ  United Kingdom

James Goerss
From: "Goerss, Dr. James" <goerss@nrlmry.navy.mil>
To: "'Heming, Julian'" <julian.heming@metoffice.com>,
     'Jeff Callaghan' <j.callaghan@bom.gov.au>, tropical-storms@tstorms.org
Subject: RE: [Tropical-storms] Equatorial disturbance

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Julian and Jeff,

NOGAPS also indicates development of this system with pretty much SW
movement.  The 12Z, July 3 analysis shows a surface circulation at about
1.5S,
161E which slowly strengthens and moves to about 9S, 152E in 72 hours
(12Z, July 6).

Jeff Callaghan
Hi Roger
I heard a report on our (OZ) ABC that 39 people were killed by landslides
on Chuuk.
What is your opinion on the latest quikscat data on the equatorial system
in the SH. Are the gales suspect due to the highly asymmetric
structure of the wind field?
Jeff
 

Robert Burke
Aloha

Using NMAP2, I am able to remove rain contaminated winds from the quickscat
data.  The most recent pass (~21Z) shows 20 kt winds in the south semicircle
of the system with 15 kt in the north semicircle.  The rain contaminated wind
field show as much as 55 kt in the south quadrant of the system. RSMC Nadi is
now calling this system TD 17F.

Aloha
Bob Burke
NWS Honolulu

Jim

Roger Edson
Robert and ALL,

I know that Jeff just asked me this, because I keep promising an update to my QuikSCAT tutorial..

Anyway, my 'idea' is shown in the attachment.

Basically, I think what Robert Burke says is correct about this system. Winds aren't much greater than
25kts on the south (higher pressure gradient) side of the circulation.  The higher winds reported in the
southwest quadrant are clearly rain-affected---and thus are too high, because of confusion in light winds
(generally, winds less than 25kts) between a rain scattering signal and a 'true' higher winds signal.

One can tell the difference in two or three ways:

1. Look up-wind and down-wind of the suspect area to see the prevailing wind speeds/flow. Does an increase
'make sense' synoptically?

2. Both the wind vector depiction (showing lots of cross-track winds) and the ambiguity
depiction--especially-- (showing 2-solution cross track winds) will give a good indication of suspected
speeds and directions.

Note: The so-called rain flags are only a first guess, SO PLEASE don't disregard until you have done a finer
(similar) analysis since many of the wind vector cells have either/or good directions or good directions and
speeds (as you can see, in some cases, if the  'correct' solution was chosen, the wind speed would
have been quite a bit less).