Several people have asked me whether what we have been experiencing in Metro Manila for at least 2 weeks can be considered as a "heat wave". Since I teach a bit of meteorology and climatology for freshies on Environmental Science 1, I had to dig up my notes and find out what the definition of heat wave is.
There is no fast and clear numerical rule for determining what a heat wave is. It is relative. For instance, in Scandinavian countries like Denmark and Sweden, three days of consecutive 28 c weather is officially considered as a heat wave by their meteorological agencies. In these northern European countries where people are used to summer temperatures peaking at 21 C, this is indeed unbearable. Visitors to London from the Southern United States laughed at a Times headline that went "London SIZZLES in the 70s. Southerners are used to having temps that reach above 100 F. In the Southern United States, two days of excessively hot weather is considered a heat wave. The National Weather Services issues the needed advisories as a result.
The World Meteorological Organization defines heat waves as "a period of at least 5 days of consecutively hot weather that is at least 5 C above the average maximum temperature". Now digging up the average max temp for the Philippine summer months for the past 20 years shows that the average max temp in May is about 32.5 C. Last year on May 14, the max temp was at 33 C. Today we expect it at 36.3-36.5 C. This is approximately 4 C from the average temperature and 3.5 C from last year's. This has been happening for at least two weeks. I safely could conclude that Metro Manila is just a degree or less than the 5 C WMO threshold for declaring a heat wave.
The agency in any other country that is tasked with announcing this climate emergency is the weather bureau. So far PAGASA has advised us that the temperatures will be above normal and all time records have not been broken as a result of El Nino but hasn't advised us about a heat alert. However judging from newspaper reports, it seems that heat related illness is on the rise and we have 1 page newspaper ads promoting sports drinks targeted not at athletes but the general public.
To compound the problem, highly urbanized cities like Metro Manila no longer experience substantial nighttime cooling as a result of heat radiated by hot built up surfaces. Thus it can be observed that the average nighttime temps could be 27-28 C. If cities have enough green spaces, the temperature may be expected to go down to at least 25 C. High daytime and nightime humidity makes the problem worse. People can't cool off since sweat can't evaporate in these humid conditions. One of our MSc students did her thesis on the Metro Manila heat island and came out with estimates that actual temps could be 3-4 C higher than what PAGASA records in its weather stations. So if PAGASA reports a temp of 37 C, the actual temp on the street could be 40 C or even higher.
In other countries, heat waves are becoming a yearly phenomenon and mortality statistics are increasing. Health authorities expect this to become worse with heat related mortality exceeding all deaths due to other climate events (tornadoes, cyclones etc). The 2003 European Heat Wave caused at least 37 K deaths and 14 K of these were in France alone.
Colleagues who have worked in desert countries have noticed that the 2010 Pinoy summer is like the usual summers in those countries. They have one experience this year which they never had in the past here. The heat stings the eyes. I have experienced this in a desert summer myself.
More frequent heat waves are predicted by several global warming models. It seems that the hot summer we have is a partner of the deluge we had last year.
The only thing we can do is to hydrate ourselves by drinking lots of water, avoid going outdoors in the hottest times of the day (10 AM - 4 PM), seek cool places and don't overexert. The consuelo de bobo in Metro Manila is that we have an oversupply of "cool shelters". We call these malls! But only until we have MERALCO power!