From: "Heming, Julian" <julian.heming@metoffice.com>
To: tropical-storms@tstorms.org
Subject: [Tropical-storms] 03W about to form?
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TC folks,

Following on from STY Mitag could we be about to see another March TC in the
North-West Pacific (Mark Lander's info posted previously on March TCs is
included below)? Latest Quikscat image is attached showing a closed
circulation and a (dubious?) 50 knot wind on the northern flank.

Regards,

Julian
 

John McBride

    This is an interesting system.  I have been watching for several days now the precursor convective squall-line, of dimension about 1000 km east-west by about 200 km north-south.  I remember thinking a few days ago" "If this had occurred during a field experiment it would be the subject of many papers in Monthly Weather Review; but since it didn't it will no doubt fade into obscurity."

Anyway, I have put the GMS enhanced imagery for the past week on my web-page.

            UTC  March 13 23000                            March 14 2300                                March 16 0000                                    March 16 2300
 

UTC March 17 2100                                    March 18 2300
 

There are no real synoptic scale features that I can associate with the system... Though there is a westward drift; so if there are any easterly-wave trackers out there, they may have something to say.  A few days ago, I was looking hard at it to see if I could ascribe it to one of those n = 1 equatorially trapped Rossby Wave's I am so fond of.  It does not show up  on Matt Wheeler's satellite-based diagnostics of the waves (though he did have an n=1 there a few days earlier).  Matt's site is at http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR_modes/JA.all.20to10.html, and I have put the some images from the current Java-loop up on my web-page  (current, 3 days ago, 6 days ago).   Looking at the winds a few days back (say 15th 000 UTC), there is a small scale westerly jet on the equator at about 140E, with weak vortices on either side; but the scale of the phenomenon is quite small compared to our "normal" concept of a westerly burst.
 

Another matter of interest in the context of this apparently developing system is its relevance to the idea of developing versus non-developing cloud-clusters.   Back in the early 80's when I did the work with Ray Zehr and Bill Gray, we used to look at the properties of developing versus non-developing cloud clusters as the belief at the time was that there were thousands of cloud clusters about, but only a small percentage developed into tropical storms.  However, when I moved out into the real-world of weather bureaus and forecasters, I was told by many that once a cloud cluster hung around for several days, it was almost certain to eventually develop into a TC.  Well..., if this one develops, it is  case in point, having had that impressive and continuous cloud signature as shown on my web-page for 6 days now.... Of course the factors working against it are the time of year and its relatively low latitude.

cheers

John McB

Roger Edson

Hi John and Julian and other TC Folks,

John, I think if you and Ray had access to scatterometer data  and microwave
imagery back in the early 80s, your conclusions about developing versus
nondeveloping cloud clusters might be quite different (specifically
regarding low level vortex development--upper level conclusions are probably
still valid).  The resolution and quality of the data, especially in these
'more remote systems'--away from the rawinsonde network,is many orders of
magnitude better now than then!  In fact (I'm sure this will be somewhat
controversial, ha ha), I think the same statement can probably be said about
the GATE data and studies (my first 'adventure' into tropical meteorology).
We are now seeing how the vortices develop and get organized, if associated
with 'surges' (equatorial or poleward), whether they are developing within a
'favorable' region or 'moving' into a favorable region, etc. Amazing stuff.

Just a comment on the scatterometer data (yes, there is a Requirement for
analysis and INTERPRETATION), the stronger winds noted by Julian are all
probably rain-enhance winds (psuedo-winds)
that primarily occur in light wind regions where the wind retrieval
algorithm gets confused by the difference between light winds in
moderate/strong rain and strong wind regions.  Fortunately for most of us
tropical analyst who look at this data every data, it is usually quite easy
to distinguish between these two types of events--even if the computer can
not.  So here are some simple rules:

1) A surface vortex must form in a light and variable wind region--not
within the strongest winds (so figure out where the trough axis is either by
wind curvature or the light winds OUTSIDE of the rain areas).

2) Strong winds inside a trough axis (especially in the early stage) are
probably rain-affected and not real.  The 'real' winds can be determined by
observing the gradient of wind intensity from outside of the rain region to
the center, however being careful not to go  all the way into the actual
trough axis.  In the case shown by Julian I would estimate winds at 20-25kt
at that time (yes, there is a 'gray' area--so, I'm not saying there isn't
any thing there).

3) USE the wind ambiguity solutions with the wind vectors to avoid falling
into the trap of misinterpreting the trough axis. This is concurrently
available on the NOAA/NESDIS QuikSCAT page (maintained by Dr Paul Chang) at:

 http://manati.wwb.noaa.gov/cgi-bin/qscat_storm.pl

Once you look at the ambiguity solutions for a while, their interpretation
becomes easier.  For one, the points where only two (2) solutions exist
(versus the "+ - like" 4), are the highest confident regions and almost
always draw into the trough axis; just avoid the isolated cases within the
light wind regions where the 2-way solutions are lined perpendicular to the
swath orientation and are rain-related (there are not many of these
situations in any image and must occur in heavy rain regions where (usually)
the winds are light).

Hope this helps....and of course, let's see how this new suspect
area/disturbance turns out. Is it a 'developer'?

Roger

Chip Guard

From: Chip Guard <Chip.Guard@noaa.gov>
To: John McBride <jmb@bom.gov.au>
Subject: Re: [Tropical-storms] 03W about to form?

John,

It's always good to get your perspective on things.  I think you are right about the
longivity of the cluster.  I think the time of year relates more to the shear and is
more important than the latitude.  The latitude, however does relegate the size of the
circulation.  Cheers mate,

Chip