April 2016 also warm

Photo of red flowers

Red flowering gum

In the whole month, only one day and seven nights were cooler than normal. Days and nights warmed together. Weekly average temperature was 4.1° above normal early in the month, and again 3.5° above normal at the very end.
Rain was recorded only on the 10th (5.8 mm) and the 11th (13.0 mm). While the early morning dew point was high only when it rained, the afternoon humidity was always high, falling below 30% only once.

Weather log for April 2016

Comparing April months

Daily maximum, minimum, and mean temperatures were all very high but not record values for April. The mean of 20.5° was beaten by 20.6° in April 2005. In that month, this month’s daily maximum (29.0°) was also beaten (29.5°). This month’s daily minimum (12.1°) was beaten by the record value of 12.2° set in 2014.
The subsoil temperature, and other variables were near normal.
The total rainfall of 18.8 mm was well below the average of 40 mm, in the 32nd percentile. However, for the sixth month in a row, there are no serious rainfall shortages for totals for any number of months. Now, the greatest shortage is the 48-month total of 2191 mm, which is in the 12th percentile. Ponds persist in Greenhatch Creek.

Climate for April 2016

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.

March 2016 had a warm dry spell

Photo of Pittosporum berries

“Native Apricots”

In the first half of March the average weekly temperature was more than three degrees above normal. Nine days had maxima above 35°, when the month usually has only one. However, no day reached 40°, as happened in March last year (20/03/15).
No rain fell in this time: the period of 43 days between February 4 and March 19 may have been the seventh longest rain-free period in 133 years. (No official record is now kept.)
Normal weather returned in the second half of the month. I recorded 20.8 mm of rain on the 19th, and further rain on the 30th and 31st.

Weather log for March 2016

Comparing March months

Despite the cool change, this was the warmest March of the new century. Daily maxima, minima, and means were all 2° above average. The subsoil temperature was also 1° high, as in March 2012 and 2013, but not as high as in 2007 (2° high).
This was not a dry month. The moisture indicators cloudiness, humidity, and (low) daily temperature range were just slightly on the dry side.
The total rainfall of 35mm was below the average of 53 mm, but in the 46th percentile, not far below the median. Again, there are no serious rainfall shortages for totals for any number of months. In fact, the five-month total of 362 mm is high, in the 81st percentile. Ponds persist in Greenhatch Creek.

Climate graph for March 2016.

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.

February 2016: hot, dry days

Photo of cooba blossom

Cooba in February

Weekly average temperatures began 2 or 3 degrees low, but ended with a long warm spell 3 degrees high, that extended into March. Days were especially hot, with the 26th reaching 41.5°, the equal second hottest February day. Nights were seldom very warm, and the early morning of the 26th was 25° cooler than the afternoon.
Few days were cloudy, none of them late in the month
Rain fell only on the 3rd, as three heavy showers of 7mm, 27mm and 13mm. The second shower, at 5pm, had the most intense rain of the new century: 27 mm in less than 27 minutes. Bureau of Meteorology data show that such a half-hour storm, yielding 1 mm of rain per minute, has only a 10% chance of happening here in any year. It is a “one in 10 year event”.

Weather log February 2016

Comparing February months

While the average temperature for the month (25.8°) was normal, the mean daily maximum, at 34.7°, was the hottest for February. A rather low mean daily minimum, (16.8°) made the daily temperature range a desert-like 17.9°. This is the widest February value, 3.5° wider than normal.
Other signs of dryness were the low early morning dew point (10.8°) and very few cloudy mornings (17%).
The total rainfall of 47mm was below the average of 67 mm, but right on the median 50th percentile: just half of all February months have been wetter. Again, there are no serious rainfall shortages for totals for any number of months.

Climate for February 2016

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.

Hot Days and ENSO

Graphical log of max temps and hot days

More frequent hot days do not come in a three year cycle, but in a 1.5 year cycle related to ENSO.

The Hot Day data set

The graph of number of hot days per year

Log of annual hot days in 16 yearsThe graph on the left is one I posted earlier. The height of each data point represents the number of hot days in a year, plotted near January. The pattern of points led me to join them by a smooth curve. This curve swings up and down rather regularly, with five peaks and five dips in the fifteen years. That is, more frequent hot days seem to come in a three-year cycle.
Is this cycle “real”? Should we look for a cause? Will the cycle continue?
Probably not! The points of measurement are one year apart. Cycles that are only three years long may be “aliases” of different and shorter undetectable cycles. (See Note below on Nyquist frequency.)

More detailed hot day data

Other graphs already shown include further data: the number of hot days in each month, and the 13-year average number of hot days in each calendar month. From these I have calculated a relative frequency. That is, the ratio of the actual number to the average number for that month.
Only the months of November, December, January and February have enough hot days to calculate a relative frequency, but these can show changes within the hotter months of each year.

The daily maximum temperature data set

A graph that I posted in “El Niño and my climate” shows a curve of smoothed monthly means of daily maximum temperature anomalies. The yearly cycle of summer-to winter temperature has been removed. I have also applied a smoothing function, which makes the monthly points of measurement effectively two or three months apart. As a result, cycles longer than about six months can be detected.
There are about 10 peaks and 10 dips in the 15.5 year curve. They define a cycle of about 1.5 years wavelength. That cycle is so much longer than the minimum-detectable six month cycle that “aliasing” is not likely.
The reality of this temperature curve is supported by its close similarity to the recognised curve of the El Niño – Southern Oscillation (ENSO), as read from NINO3.4 Pacific Ocean sea surface temperature anomalies.

A combined graph of hot day and temperature data

The graph at the top of the page presents the monthly smoothed maximum temperature anomaly again, using the scale at the left. To this I have added data on the number and frequency of hot days.
The annual number of hot days is shown in blue, in blue boxes. The boxes are placed higher or lower according to the number, but the height is adjusted to match other data better.
A “Hot Day Index” is shown by blue diamonds. This index is based on the relative frequency of hot days in each month that has data.  I have re-scaled the values to improve the match. (See Note on Re-scaling below.)

Matching hot days with temperature

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Manilla’s Hot Days to June 2015

Log of annual hot days in 16 years 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”.

Note added.

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

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March 2015 was hot

Photo of bird in a gum tree

Blue-faced honeyeater in a White Box tree

March had 5 hot days over 35°: more than January (2) or February (3), but less than December (7) or November (10!). On the 20th the temperature reached 40.0°, making it the hottest March day of the century, 10.2° above normal. It came in a warm spell, with a weekly mean temperature 3.6° above normal. Some days had extremely low humidity, with afternoon values below 10%. The morning dew point on the 28th, minus 4.2°, was the lowest March value.
There were five rain days, with the highest reading 22.0 mm on the 12th.

Weather log for March 2015

Comparing March months

The average daily maximum temperature, at 31.8°, was the hottest of any March in this short record. It was almost the same as in each of the months of this summer, but not as high as that of last November (33.9°). The daily mean temperature (23.6°) was also the highest for March, just beating the 23.4° of March 2000. Night temperatures were normal, making the daily temperature range wider than normal. The mean early morning dew point of 8.3° was a record low value.
The total rainfall of 35.8 mm, while well below the average of 53 mm, is quite normal. It is in the 46th percentile: nearly half of all March totals were lower. Among rainfall totals for more than one month, there is little change. Again, the only serious shortage is in the 24-month total, which is now in the 5th percentile.

Climate for March 2015

Data. Rainfall data up to 26/3/15 is from Manilla Post Office, courtesy of Phil Pinch. Temperatures, including subsoil at 750 mm, and other data are from 3 Monash  Street, Manilla.

Spring 2014 dry and hotter

Weather log for spring 2014

Warm weather developed in early October, followed by a cool spell with one rain day of 26.4 mm. After that came three hot spells. There were showers and storms in the district, but little more rain fell at Manilla.
This spring was slightly hotter than spring 2013 and spring 2009, but not as hot as spring 2002. The air was not as extremely arid (dew point 3.6°) as in last spring (dew point 2.3°), and skies were a little more cloudy.
The total rainfall of 69.8 mm was in the 8th percentile: the 10th lowest spring rainfall. (Spring 2002 had been equal 5th lowest at 66 mm, and spring 1957 the lowest at 23 mm.) Rain fell on 11 days: more than in spring of 2002 (9 days), but fewer than in 2013 (13).

Climate for spring 2014

Data. Rainfall data is from Manilla Post Office, courtesy of Phil Pinch. Temperature, including subsoil at 750 mm, and other data are from 3 Monash Street, Manilla.