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.
The first 30-degree day of the season came on the 3rd. That was ten days late, but the first 35-degree day followed soon after, on the 6th. Most days and nights were warm through the month, and the weekly mean temperature was three or four degrees above normal until the last week.
Ten sunny days were followed by days with much more cloud, and four rain days (usually seven). On the 22nd and 23rd, I recorded 17.4 and 8.0 mm.
Comparing October months
This was the warmest October of the new century for all daily temperatures: maximum, mean and minimum. The mean temperature of 21.7° was 3° above average, and much higher than in the other warm Octobers of 2014 (20.6°) and 2007 (20.4°).
The graph shows the curious fact that October months have warmed steadily since 2011. Since 2012, Octobers have not become drier: rainfall, cloudiness and humidity have increased rather than decreased.
The rainfall of 35.0 mm was below average, in the 29th percentile. As in last month’s report, there are no serious shortages in rainfall totals for small numbers of months. The only serious shortages are in the 30 month total (6th percentile) and in the 42 month total (7th percentile). There are still deep ponds in Greenhatch Creek.
Data. 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.
Parametric plots of smoothed climate variables at Manilla
“October 2015: very warm”
October raw anomaly data (orange)
After a cool September, October was very warm: the warmest of the new century in both daily maximum and daily minimum. The daily temperature range was also high, but the soil temperature was not. Rainfall remained rather low, while cloudiness and dew point were near normal.
[The recorded anomaly values for daily maximum and for daily minimum were +3.2° and +2.2° respectively. For convenience, I have plotted them 0.2° lower.]
Fully smoothed data (red)
In the latest fully smoothed data (April 2015) all trends on the first four graphs continued to move steadily away from drought. The daily minimum temperature anomaly began to rise, and subsoil temperature rose faster.
Fully smoothed data – Gaussian smoothing with half-width 6 months – are plotted in red, partly smoothed data uncoloured, and raw data for the last data point in orange. January data points are marked by squares.
Blue diamonds and the dashed blue rectangle show the extreme values in the fully smoothed data record since September 1999.
Normal values are based on averages for the decade from March 1999.* They appear on these graphs as a turquoise (turquoise) circle at the origin (0,0). A range of anomalies called “normal” is shown by a dashed rectangle in aqua (aqua). For values in degrees, the assigned normal range is +/-0.7°; for cloudiness, +/-7%; for monthly rainfall, +/-14 mm.
* Normal values for rainfall are based on averages for the 125 years beginning 1883.