Gedday,

 I have been away over the past two weeks; so I missed all the excitement of the development and subsequent course of the two TC's in the North West Pacific. It was also good to see Johnny's new tropical discussion web-page.

It seems the double genesis event that occurred at longitudes about 135 and 155 close to 00UTC 29 June were related to a westerly wind burst/MJO event.  The El Niño monitoring people are talking about the westerly wind burst that occurred in late June.  To check up on them I had a look at the TAO/TRITON data display page; and one of their standard charts is reproduced on my web page (synoptic discussion - today's date). The chart is the set of three hovmollers of anomalies along the equator of zonal wind, SST and 20C isotherm depth, taken from the TAO/TRITON data display page (http://www.pmel.noaa.gov/tao/jsdisplay/).

You can see on the left-most panel (zonal wind)  a clear westerly anomaly of about 5 m/sec around longitude 150-160E in late June.   To look at it in more detail, I pulled out some higher resolution Hovmollers of zonal wind and zonal wind anomaly along the equator from the CDC global circulation and anomalies page (http://www.cdc.noaa.gov/map/clim/glbcir.shtml) .

Both the wind and the anomaly hovmollers show a clear westerly event developing at on the equator at 135E on about 19 June and subsequently propagating eastward to be at about the genesis longitudes between 28 and 30 June.  Looking further at the Hovmollers, the original westerly anomaly had its origin further west in a monsoon westerly burst at about 70E on 7 June; and this is supported by Matt Wheeler (Boy wonder)'s real-time OLR diagnostic  (http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR_modes/h.6.ALL.EQ.html) which shows an  MJO event beginning round 70E on June 2-3 and propagating to be at the genesis longitudes of 135 - 155 E on 28 June - 1 July.

 

It is interesting to look at the evolution of the daily 850 hPa charts during the event.  On my web-page I have put these up for 22, 26 28 and 30 June. On 22 June, the wind burst was a very small and discrete pulse, of scale about 10 degrees lat by 15-20 degrees longitude located at about 5, 135.  By the 26th it had come up against the trade easterlies in the location of the monsoon trough and had grown in lateral extent.  The impinging of the westerly surge on the equator against the higher latitude trades led, in subsequent days, to the development of  very strong -partial U/partial y vorticity in the location of the trough, thus leading to some sort of a shearing instability whereby two discrete vortices spun up.