The heat waves of this summer were several degrees cooler than those of last summer (2016-17). Also, unlike last summer, there were several cool spells between them. Arid spells with extremely low dew points came in mid-January and mid-February.
While last summer had 12 very hot days (over 40°), this summer had only 4; even fewer than in the summers of 2013-14 (5), 2003-04 (6) or 2002-03 (5).
For most of the season, as falls of rain were light, and came at increasingly long intervals, the soil became very dry. That changed on 25 February, which had rainfall of 54 mm.
While this summer is the second-hottest of the new century in Manilla, its mean temperature (26.6°) is a degree below last summer’s 27.6°, and close to that of 2005-06 (26.3°). The subsoil temperature has been low (24.6°) in each of the last three summers. Two other measures have held steady, but a little high: cloudiness at 38%, and daily temperature range at 16°.
While the mean dew point is lower (less humid) than in last summer, the total rainfall is higher. At 140 mm (estimated), the rainfall is still well below the summer mean of 227 mm. It is at the 20th percentile, perhaps the 25th driest summer from 1883.
Data. A Bureau of Meteorology automatic rain gauge operates in the museum yard. From 17 March 2017, 9 am daily readings are published as Manilla Museum, Station 55312. These reports use that rainfall data when it is available. That gauge failed (again) on the 25th of September 2017, and later readings are from my non-standard gauge.
All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.
This summer, like summer 2013-14, was marked by repeated heat waves. The first, early in December, was brief. Another, in mid-January, led into one that was hotter, and persisted through the first half of February. On a weekly basis, temperatures did not fall below normal at any time in the season. Mid-February had the two hottest days of the new century, at 44.9° and 43.8°.
Although there were as many rain days as usual (22), only two days had rainfall exceeding 15 mm, and there was almost no rain in February.
Comparing summer seasons
Mean temperatures set new records for the summer season: daily maximum 35.6°, average 27.6°, and daily minimum 19.7°. Each of these was more than a degree higher than the old record. Nearly all such figures for the months December, January, and February had also been records. However, the subsoil temperature for the summer (24.7°) was low.
Two indicators of moisture were a little low: mean early morning dew point (13.4°) was down 0.7°, and mean daily temperature range (15.9°) was 0.8° wider than usual.
The percentage of cloudy mornings (38%) was almost the same as in the last four summers, and lower than in the previous two. However, 38% is much more cloudy than the “normal” figure of 31% cloudy mornings that was set in the decade 1999-2008. Summers were more sunny then.
This summer’s rainfall was very low. The unofficial total of 101.4 mm would place it as the seventh driest on record. As shown on the graph, summer 2013-14 was drier (85 mm). Otherwise, there has not been a drier summer in the half-century since 1964-65 (70 mm).
[The following summer (Summer 2017-18) was not as hot and had more rain.]
Data. Rainfall figures are usually from the automatic rain gauge at Manilla, published on the internet by the Bureau of Meteorology as Station 55031. However, the gauge ceased recording five months ago (8/10/16), and this month’s readings are from my non-standard gauge. All data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.
San Pedro cactus blooms
Taken as a whole, this summer was nearer to normal than last summer. Several numbers were close to average: daily maximum temperature, daily mean temperature, daily minimum temperature, and daily temperature range. The mean early morning dew point was rather low, while the cloudiness and total rainfall were a little high.
There were two very hot days over 40° (the usual number) and 29 hot days over 35° (just 6 more than usual).
A very cool spell came in early December, between other cool spells in late November and late December. Then, from mid-February through to early autumn, the weather was very warm. With this warmth came dry air, a wide daily temperature range, and sunny skies.
The total rainfall of 253.6 mm was above the summer average of 227 mm. After 20 rain days (the usual number), rainfall ceased on the 4th of February. Had it continued, the total might have reached a very wet 350 mm.
All data, including subsoil at 750 mm, are from 3 Monash Street, Manilla. Rainfall data up to 26/3/15 is from Manilla Post Office, Station 055031.
This post updates a similar one by including three more years to make a total of sixteen. It is in the same format as a recent post on Manilla’s frosts. Because the summer, which has the most hot days, crosses from one calendar year to the next, I have begun each year at July. I have called days warmer than 35° “hot days”, and days warmer than 40° “very hot days”.
I have analysed the pattern of hot days in more detail in a later post “Hot days and ENSO”. By finding the relative frequency of hot days in all of the hotter months, I show that there is a cyclic variation related to ENSO. The cycle period is near 1.5 years, not 3 years as the log of annual frequency of hot days (above) suggests.
Graphical log of hot and very hot days
The first graph is a log of the number of hot and very hot days in each year. The three years with the most hot days had almost the same number: the year ’02-’03 had 41, the year ’09-’10 had 44, and the year ’13-’14 had 43. The two years with the fewest were ’07-’08 which had 5, and ’11-’12, which had only 4. The 13-year average is 26. Counting only the very hot days, ’03-’04 had the most (6), and four years had none at all. On the average, two days exceeded 40° in a year. (These are thirteen-year averages, not updated.) The number of hot days per year seems to have a cyclic pattern, with a period that increases from two years to four years during this short record. This is just a curiosity. The pattern of hot days has a lot in common with the pattern of smoothed monthly temperature anomalies for all months. These are plotted here, on a graph that relates them to ENSO. The relation of Manilla daily maximum temperature to ENSO was quite close from 1999 to 2011, but failed almost completely since mid-2011. In the earlier post on frosts, no cyclic pattern can be seen, nor any relation to ENSO.
New Record hottest days
In the sixteen years, there have now been 37 days hotter than 40 degrees: that is, 2.4 days per year. It remains true that December has fewer very hot days than November or February. A new record was set on 12/1/2013 by a daily maximum temperature of 43.2 degrees, beating the 42.6 degrees of 20/11/2009. This record was broken again on 3/1/2014, with 43.7 degrees. In the latest year, the hottest day (41.1 degrees) ranked only 12th, and it was not in summer, but in November.
Three new annual graphs
Commelina cyanea in Monash Street
This summer, January was no warmer than December or February, and none of these months was as warm as November! The number of hot days (over 35°) had a similar pattern that “sagged” in midsummer: Oct: 4 days; Nov: 10 days; Dec: 7 days; Jan: 2 days; Feb: 3 days; Mar: 2 days (in the first week). There were no very hot days over 40° this summer, although there had been three in spring.
A very cool spell from late January to early February had day and night temperatures 4.5° degrees lower than normal. Humidity was also low at that time and earlier, in mid-December.
By most measures, this was a normal summer. Compared with the 21st century average, the daily maximum temperature and the daily temperature range were both just one degree low, and skies were a little more cloudy. The dew point (humidity) was low, but much higher than last summer.
The rainfall of 224 mm could hardly be more “normal”. It lies between the 125-year average of 227 mm and the 125-year median value of 221 mm. Summer rainfall totals like this also occurred in 2002-03 (227 mm) and 2008-09 (229 mm). Historically, summer rainfall totals in the “normal” range from 220 mm to 230 mm occurred in 1902-03, 1917-18, 1936-37, 1948-49, and 1957-58.
Data. Rainfall data is from Manilla Post Office, courtesy of the Post-master, Phil Pinch. I thank Phil for his help over the years. When he retires this March, there is some uncertainty about the future of rainfall observations that have been maintained for 132 years since March 1883.
Temperature, including subsoil at 750 mm, and other data are from 3 Monash Street, Manilla.