For those of you interested in things tropical (I still am).

The convective activity has been building up over the equatorial Indian
Ocean during the last few days as an MJO seems to be developing (see the
Weekly Tropical Climate Note issued yesterday).

Up till about yesterday the convection seemed to be jumping around as it
usually does, but by and large centred around the equator.  Interestingly
the Darwin tropical analyses show weak equatorial easterlies at 850 hPa
across much of the "Maritime Continent", and at 200 hPa even some
equatorial westerlies across Borneo show up.  This is significant since
there are almost permanent easterlies over this area.  All of this suggests
Kelvin wave response to the east of the Indian Ocean convection, however at
both levels there is a tendency for the wind strength to increase away from
the equator rather than decrease so there are other things happening.

The other thing to note is that bifurcation appears to be happening over
the Indian Ocean between about 70E and 80E, that is the convection is
splitting into two large areas either side of the equator.  The winds at
200hPa and 850 hPa in particular are showing signs of the Gill type Rossby
response.  Should this continue then these will turn into vortices which
should move away from the equator towards the poles.  We will see!!  Then
we may see quite a rapid increase in the convection over the Maritime
Continent which normally happens following the bifurcation according to
what seemed to happen on a number of occasions in the 1990s.

Mark

Matt Wheeler

Mark and others,

You're correct about it being quite a sustained "blow-up" of convection over the equatorial Indian ocean. For a perspective
from the OLR, see
http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR_modes/h.6.MJO.EQ.html (Captured image for this date)

And you are right about there being a nice Gill-type response to
it in the winds.
http://comms.ho.bom.gov.au:80/tlaps/charts375/wind850R_0.gif (Captured image for this date)

However, I don't think this necessarily means a bifurcation of the convection to the north and south.
MJO composites that I makesuggest a slow shift of the convection to the east is a more robust
result. Certainly a bifurcation happens sometimes, but not all times (but neither does an eastward
movement!). We'll see.

Another thing we should be looking out for now is a north-west cloud band. It is the right time of year,
and the convection inthe eq Indian ocean has been shown to often be a good precursor.
Mark, what else was it that you looked for when you were a SA forecaster for these NWCBs?

As for those El Nino watchers, if you are hoping for another westerly wind burst in the west Pacific to
spark a oceanic Kelvinwave, then this particular MJO (the one with its enhanced phase in
the Indian Ocean), shouldn't give any westerly winds in the W. Pacific for another 2-4 weeks,
given the forecast of the first plot shown above (remember that the surface westerlies slightly lag the
enhanced convection of an MJO, so the convection needs to be out near 160E to 160W before it can
give westerlies in the WP).

-Matt.

Roger Atkinson
Hi Mark et al,
Just happen to be sitting in Singapore at the moment, forecasting for a RAAF  deployment. Yesterday
was a public holiday here so we had a day off and I slept all day so missed what was going on, but the
day before (Tuesday 30 Apr) I can confirm that midlevel steering here was westerly (unforecast by
any of the models, by the way, though TLAPS forecast fields indicated a small midlevel eddy to the east
of us over SW Borneo, with w'lies to its north. This is the only case in the last two weeks where the steering hasn't
been easterly. Haven't yet had a chance to fully assess what's going on here today, though I note the DMSU forecasters have punted for E'lies at midlevels over the South China Sea.(Comments from DMSU?)
More later if time permits. Second sortie's just been scrambled so I better get back to it.
Cheers,
Roger Atkinson
RAAF 75Sqn Detachment
S'pore

Mark Williams

Matt and others.

I agree on the possibility (probability) of a NW Cloud band coming out of this episode.  It's the right time of the year.  Whether or not it will bring any worthwhile rain or just propagate as high level cloud is the question.

I was a forecaster in Adelaide in the late 60s early 70s (yes, that long ago) and there were no satellite pictures,
models or anything like that.  The forecasting rule of thumb which operated at the time was "if the
700mb wind at Cocos Island was NW at 10knots or more it will rain in Adelaide in about 4 days time"
That simple!!  And it worked pretty well as far as I can remember, at least the middle level could usually got fairly
thick.

Looking at last night's tropical charts I note that the 700mb wind in the vicinity of Cocos Is is tending northerly as a
result of the circulation south of the tropical heating and a very deep mid latitude disturbance WSW of WA which
seems to be "connecting" to some degree.  So it will be very interesting to see how this all evolves.

Mark