Watching the girls, an overhead sun, once a year

Solar noon.

Yesterday the noon sun was directly overhead at noon, allowing for this fine photo (which I am sorry to say I did not take). This is a once-a-year event (usually) because the other day when it occurs, in August, is usually cloudy. But today the sky is clear with no sign of rain, so the heat may continue to increase.

Hot season peak

Yesterday one of my neighbors remarked that the heat this year was the worst in her experience in Thailand, and there were similar comments around the table at a neighborhood Thai restaurant where last night we enjoyed drinking some Singha beer and eating a light but tasty gaprow with some friends.

We know that the Songkran holidays and the peak of solar intensity (when the noon sun is directly overhead), both come along in late April,  marking via astrology or astronomy, respectively  the peak of the hot season in Bangkok. But this does not mean that the worst discomfort is necessarily over in late April. I surmise that a certain amount of thermal momentum and also the time of onset of clouds and rain are major factors in thermal misery and this can be seen in this graph of maximum daily temperatures, shown in red. It is evident that in especially bad years like 1983 the temperatures kept rising after the quarter point of the year in late April. In other years they are truncated earlier. The reasons for the truncation are a big factor in how bad we perceive the hot season and are worth further exploration in this blog.

Yesterday, April 27, the sun passed directly overhead at noon (i.e. the declination of the sun and Bangkok itself being at 13.7 degrees), which yields a theoretical maximum solar noon intensity. There were no shadows at noon. Interestingly or coincidentally, the clouds are building today. According to my reckoning, if the rains don't arrive soon, the discomfort is likely to increase even further over the next couple of weeks.

Waiting in the heat for the rain

People interested in weather tend to be number people; I am one myself. So I am going to bring you some stats from time to time. Right now we are experiencing some hot weather, but today I see some big clouds in the morning and yesterday my taxi driver said he smelled rain on the way. Based on the wonderful dataset of weather from 60 years at Don Muang -- some 22000 days of records -- the annual march of heat and rain are shown on the chart. We see that maximum daily temps have a ceiling of about 40 deg C (we had a 39 last week). This is 104 deg F. But after mid May we see high temps are increasingly rare. Meanwhile rains enough for local flooding can occur as early as March but are most likely in May or June. The rains put an end to the high temps. To my surprise the rains in April through June  are statistically more likely to be larger than the rains later in the season, beginning in September.

This year I have found the outdoor heat to be particularly overwhelming, even though it is not statistically exceptional. A matter of age?

In days past when I lived in Isan some fifty years ago, Songkran was followed by weeks of sultry heat -- more severe than Bangkok -- when people often slept away the afternoons beneath their houses. The land was dry and cracked, the air smoking with burned rice stalks, and everyone stored up energy for the rains which turned the rice paddies to soft black mud which allowed for ploughing and planting.

Orwell had it right on today's awful heat

Here is George Orwell describing days like today in Bangkok (but in Burma):

The heat was growing worse and worse. April was nearly over, but there was no hope of rain for another three weeks, five weeks it might be. Even the lovely transient dawns were spoiled by the thought of the long, blinding hours to come, when one's head would ache, and the glare would penetrate through every covering and glue up one's eyelids with restless sleep. No one, Oriental or European, could keep awake in the heat of day without a struggle. -- George Orwell, Burmese Days

My vote for the worst aspect is the white glare, inescapable. In fact, by eliminating that and using the thermal mass of my condo, I have no inclination to turn on the air conditioning even in the late afternoon. 

But outside....miserable!! 

Next entry I will show the relationship between the continuing ascending heat and the hoped-for rains.

Record temperatures in Bangkok this week?

Don Muang airport maximum daily
temps higher than 38C (102F) since 1951.

So how is Songkran, the hot season water festival week looking in regard to Bangkok hot weather this year ? Yesterday temperatures reached 39 degrees C (102F) at the old Don Muang airport, and the historical record I got from the Department of Meteorology shows that this is not a common occurrence, it happens in about 1 in 4 years over the last 65 years (1951-2013). But then, it is not all that special either, there are a fair number of readings over 39.5 and a few even over 40, especially in the late 1990s.

Do you see a long time trend in maximun temps at Bangkok here? I don't. But then, given the urbanization around the airport, which was surrounded by rice fields when I first arrived here in 1963, we should be surprised that there has not been a steady upward march of hot recordings over the past half century, even aside from any global warming, it having been known for a century that urban areas are generally warmer by 5 degrees or so than country areas.

So if we are looking for evidence of global warming in this record we are not finding it. It is worth considering that most of the records which people are using in this heated debate over temperature trends are also taken in and around airports. Do "climate scientists" pay much attention to microclimate?

For that matter if we are worried about human misery in the tropics, we should look at other weather indications like dew pount which better reflect our capacity to survive in hot weather. We die at dew points of 35 because we cannot dump heat at that level.

The southerly breezes in Bangkok were recently -- about 2 hours before -- flowing northward over the Gulf of Thailand, so along with local microclimatic ground heating from paving and other materials that capture heat, we should look to surface sea temperatures in that shallow gulf for explanations of downtown or airport temperatures.

Radiative cooling in the humid tropics II: special for psychrometriphiles

Today's entry is the second in an ongoing series on radiative cooling for the tropics and is mainly for readers who understand psychometric charts. I show today's very typical hot season trajectory of Bangkok air properties from dawn to mid afternoon (red arrow) superimposed on a handy old chart I use to aid my judgment on matters of thermal comfort.  The daily process is essentially isenthalmic (constant-enthalpy). Our Bangkok day is way outside of US standards of comfort (with which I disagree) and also within the "danger zone" (justifiably so) that was established by the US military after scandalous heat deaths of marine recruits during basic training. Having also done my basic training in the sweaty Virginia summer near Richmond, I am proud to have survived at least the heat battle of a forced march before reforms were instituted (but I recall an ambulance did trail our ragged column), though I never did hear a shot fired in Vietnam.

Today's Bangkok wet bulb temperature (surrogate for enthalpy) was 28C (82F). Wet bulb temps above 30 were recorded with deadly results in Pakistan last year and are considered very dangerous in military training. The wet bulb temp should be close to the surface sea temp (also 28 in the Gulf of Siam as recorded yesterday) and has never been seen to exceed 35. Wet bulb temps of about 32-33C have been recorded in Bangkok and also (surprisingly) in the middle of cornfields in Appleton Wisconsin. Our wet bulb today is about at the 1% summer design level for US hotspots such as Pensacola, Galveston, and El Centro.

Note from the chart that the afternoon and evening dew point temperatures drop to about 25C  and relative humidity to 50% so a cooled surface at that temperature would not attract condensation.

Damp laundry in the morning heat

This hazy warm morning  at 7:30 am while checking my still damp laundry (high humidity at dawn) I measured a wet bulb temp of 28.2C (82F), as high as I can recall here in Bangkok. The daily pattern has been the same for a week now, typical hot season weather. Humid dawns with air, wet bulb, and dew point temperatures converging at about 27-28C, followed by warming  to about 38C (100F) midafternoon. Increasing relief from southerly breezes off the Gulf of Siam throughout the day and evening, offsetting to some degree the rising temperature. Much like late summer Gulf Coast Texas weather. Greater afternoon discomfort has more to do with glare and radiant heat from hot streets and sidewalks  than 100F air temperature. Average daily temps about 33C. Checking back over the years records I find that it was a bit warmer in the early 1990s, with daily average temps sometimes 34 or above, hence whatever people want to think we are not experiencing anything extraordinary so far this year. For the last week, check out this chart from Weather Underground (note the superelevated bump in dew point this morning):

April 2016, typical hot season, breeze from the south