FURTHER UPDATED 28/09/2019 14:20 AEST
If you want to find out why go to the following post:
On the 21 September 00:00 UTC, the equatorial trade winds in the Western Pacific are still dead, as far east as 165W!
Shown below are the Sea-Surface Temperature Anomalies (SSTA) for the 6th of September 00:00 UTC (on the right) and the 21st September 00:00UTC (on the left).
Note that warm surface water in the Western Pacific has moved eastward by ~ 3,300 km in 15 days.
The battle in between the warmer waters in the Western Pacific and the cooler waters in the Eastern Pacific Oceans.