Originally posted by joe yap
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Just got up and finish breakfast, a little sleepy still but will give it a short, Please forgive me if it is less accurate than the truth, getting old, grey matter turning white...all the wikipedia and internet fan, well, do check also.
As far as I rememeber, the trade winds (NE and SE) monsoon is separated by ITCZ (intertropical convergence zone) This boundary, if you will, will move north and south following summer. If you are north of the zone you get NE trade winds, if you are south of it you will experience SE.
In our region, The ITCZ moves as far north as Beijing in northern summer and as far south as Darwin during southern summer. Singapore being near equator, the ITCZ passes thru Singapore a few times every year. You know the ITCZ is passing thru when we have prolong showers, with very little wind for a few days, then as suddenly as it come, it stops and the sun shines again, this is typical of ITCZ passing thru. The ITCZ can be over 200 miles wide in the tropical region as such it can take a few days for it to pass. Also due to geographical topography of SEA, we dont get SE but SW monsoon.
Therefore, you do not need full northern winter to experience NE trade winds, just cold enough for the ITCZ to move sounth of Singapore, then the NE will prevail. However the wind will be strongest during the peak of winter/summer. These wind are very strong and very reliable, hence the TRADE winds, traders have used these wind for centuries for trading.
We have obvoiusly past the start of spring/autumn where ITCZ is around singapore moving south, so we should be in the NE trade wind.
This pass few 2 weeks, we had really heavy storms and long period of continuous rain, followed by sunlight and rain again, that could have been the ITCZ passing thru. This few days, wind is still and hazy, this may mark the end of passing of ITCZ. Ever so slowly NE monsoon is creeping in. Runway O2 in changi is in use again this morning as I type.
So there you have it. 10 year old residue info from the college days. Please go easy if the info is less than 100%, I am a little bored and since Joe ask the question (may have been rhetorical) I thought I will share what I know. Hope it is useful to some, at least.
cheers.
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