10-day forecast for Ho Chi Minh City on 30 March 2022 -- Centigrade temperatures
The monsoon is defined as the seasonal periods of prevailing wind in South and Southeast Asia. There are two monsoon seasons in southern Vietnam, corresponding to the seasons in Southeast Asia in general. The summer monsoon winds blow from the southwest, usually between mid-May and mid-October, while the winter monsoon winds blow from the opposite direction, from the northeast, from mid-October to mid-May. I have observed that the wind changes within one day between the seasons, and I have been tracking the dates of the wind changes for the last five years. Normally, once it changes, it stays that way consistently every day until the next season. As the normal change dates approach, I start scanning the skies to see which way the upper-level clouds are running.
The average date over the past five years in the Springtime for the Summer monsoon to begin is around 15 May. The average date for the wind change to the Winter monsoon is around 20 October, and has a higher range of variability than the close range of the Summer monsoon change.
Normally I would begin to scan the skies around 1 May. You look for the direction the upper-level clouds are running. The lower-level clouds are too variable, especially during approaching thunder storms. But this year, I noticed on 12 April that the winds had already shifted. I reviewed weather history data to determine that the wind shift must have occurred on 8 April this year. That makes it over a month early.
This is consistent with the early onset of the rainy season that we have been experiencing this year. I have observed that the rainy season (defined as rain at least every other day consistently for at least two weeks) usually starts three or four weeks in advance of the date of the monsoon wind change. The rainy season in southern Vietnam usually begins around 1 May and ends around 1 November. There are occasional rains during the normal dry season from November through April. But this year, the rainy season began in early March, making the rainy season two months early this year. The rainy season also begins with spectacular thunder and lightning storms, and we have had those in abundance through March until now in April.
My unscientific theory is that global warming has increased the width of the equatorial climate zone so that Ho Chi Minh City is now in that zone rather than the tropical monsoon zone. Thus the weather pattern in Ho Chi Minh City is beginning to look like Singapore’s. That is not good news for me.
I have not studied meteorology, so these observations and theories could be far off. I would be happy to consider any dissenting comments in the hopes of learning more about these phenomena.
