Monthly Weather Review Northern Territory April 2013 Monthly Weather Review Northern Territory April 2013 The Monthly Weather Review - Northern Territory is produced twelve times each year by the Australian Bureau of Meteorology's Northern Territory Climate Services Centre. It is intended to provide a concise but informative overview of the temperatures, rainfall and significant weather events in Northern Territory for the month. To keep the Monthly Weather Review as timely as possible, much of the information is based on electronic reports. Although every effort is made to ensure the accuracy of these reports, the results can be considered only preliminary until complete quality control procedures have been carried out. Major discrepancies will be noted in later issues. We are keen to ensure that the Monthly Weather Review is appropriate to the needs of its readers. If you have any comments or suggestions, please do not hesitate to contact us: By mail Northern Territory Climate Services Centre Bureau of Meteorology PO Box 40050 Casuarina NT 0811 AUSTRALIA By telephone (08) 8920 3813 By email [email protected] You may also wish to visit the Bureau's home page, http://www.bom.gov.au. Units of measurement Except where noted, temperature is given in degrees Celsius (°C), rainfall in millimetres (mm), and wind speed in kilometres per hour (km/h). Observation times and periods Each station in Northern Territory makes its main observation for the day at 9 am local time. At this time, the precipitation over the past 24 hours is determined, and maximum and minimum thermometers are also read and reset. In this publication, the following conventions are used for assigning dates to the observations made: Maximum temperatures are for the 24 hours from 9 am on the date mentioned. They normally occur in the afternoon of that day. Minimum temperatures are for the 24 hours to 9 am on the date mentioned. They normally occur in the early morning of that day. Mean temperatures are the average of the daily maximum and daily minimum temperatures. Daily rainfall is for the 24 hours to 9 am on the date mentioned. This means a significant fraction of the rain may have occurred on the previous calendar day. Monthly rainfall is for the period from 9 am on the last day of the previous month to 9 am on the last day of this month. Maximum daily wind gusts are in the 24 hours from midnight to midnight. Climatological values The climatological averages shown in the text and tables are generally long-term means based on observations from all available years of record, which vary widely from site to site. They are not shown for sites with less than 10 years of record, as they cannot then be calculated reliably. Climatological extremes are generally taken from available observations from all available years of record. The number of years can vary substantially from site to site. The ACORN-SAT dataset is being used for temperature area averages from December 2012 onwards. The major change from earlier datasets is that the ACORN-SAT dataset commences in 1910, rather than 1950, and hence rankings are calculated using a larger set of years. Copyright © Commonwealth of Australia 2013 This work is copyright. You may download, display, print and reproduce this material in unaltered form only (retaining this notice) for your personal, non-commercial use or use within your organisation. Apart from any use as permitted under the Copyright Act 1968, all other rights are reserved. Requests and inquiries concerning reproduction and rights should be addressed to Commonwealth Copyright Administration, Attorney General’s Department, Robert Garran Offices, National Circuit, Barton ACT 2600 or posted at http://www.ag.gov.au/cca. Product code IDCKGC12R1. Prepared on 5 June 2013. ISSN 1836-392X Cover photograph Sunset shines on altocumulus near Anningie. Photograph by Gavin Heathertington-Tait, 23 April 2008. Used with permission. If you have a photo you think would make a good cover for the Monthly Weather Review, please contact us at the address above. Monthly Weather Review Northern Territory April 2013 Overview • An active monsoon brings rain during the Easter Significant weather weekend • Temperature at Darwin Airport drops below 20 °C Some rain for the Top End after a unusually for the first time in 2013 dry season • Last hot spell for the Alice before winter On the 1st, an active monsoon brought some much-needed rain to the northern parts of the Northern Territory. This however, was short lived Extremes in April 2013 and the build-up conditions that have dominated this wet season were soon back across the Top End. Hottest day Although it was a very brief event, it managed to (Highest daily maximum temperature) bring considerable amount of rainfall, specially to the 40.2 °C at Rabbit Flat on the 22nd western Top End where a few stations broke their Warmest days on average highest daily rainfall record for April. (Highest mean daily maximum temperature) 36.6 °C at Bradshaw Darwin Airport drops below 20 °C for the Coolest days on average first time in 2013 (Lowest mean daily maximum temperature) On the early morning of the 13th, the temperature at 29.2 °C at Arltunga Darwin Airport dropped to 19.4 °C, the first Coldest day sub-twenty since 10 September 2012. Nights below (Lowest daily maximum temperature) 20 °C is a good indicator comfort level during the dry 23.8 °C at Curtin Springs on the 24th season. On average the temperature will drop below Coldest night 20 °C around 51 times in the Darwin area in the dry (Lowest daily minimum temperature) season (May through September). For the 4.1 °C at Arltunga on the 27th temperature to drop below 20 °C in April is a little Coolest nights on average more unusual. On average the temperature will drop (Lowest mean daily minimum temperature) below 20 °C between 0 and 1 time each April. The 12.6 °C at Alice Springs Airport last two years each saw two nights below 20 °C in Warmest nights on average April. The highest number of nights below 20 °C in (Highest mean daily minimum temperature) April is 5, this occurred both in April 1945 and April 26.8 °C at Cape Don 1965 at Darwin Airport. Warmest night (Highest daily minimum temperature) A hot spell for the Alice before the winter 28.5 °C at McCluer Island on the 5th A weak pressure gradient in central Australia on the Warmest on average overall 14th allowed temperatures to climb to the low 30s in (Highest mean temperature) Alice Springs. Although 30 °C and above is common 30.3 °C at Cape Don in the area during the summer months, its not Coolest on average overall common during late autumn where the average (Lowest mean temperature) temperature for Alice Springs is 28.2 °C. After a 21.3 °C at Arltunga couple of days of calm conditions, temperature Wettest overall soared to 37.0 °C at the Airport, which is 9 °C above (Highest total rainfall) the norm for that time of the year, before a 424.8 mm at Thorak Cemetery widespread cool change swept in from the west on Wettest day the 22nd. (Highest daily rainfall) 389.2 mm at Thorak Cemetery on the 2nd Highest wind gust 83 km/h at Borroloola on the 16th page 1 Monthly Weather Review Northern Territory April 2013 Synoptic summary As the month began the monsoon trough was situated over the western Top End with a low pressure centered over the Joseph Bonaparte Gulf. Most of the western Top End experienced heavy rainfall and monsoon conditions for the first three days of the month. Another synoptic feature at the beginning of the month was a large high pressure area over the Bight which kept the southern NT dry. As this low pressure area in the north moved to the west, most of the wet weather moved with it and the Top End entered a break period in the monsoon. Meanwhile, the high in the Bight moved east and a surface level trough moved across the southern NT bringing light rain to the Alice Springs District toward the end of the first week of the month. Around the 10th and 11th, the monsoon trough off the north coast dipped south over Cape York, the Gulf of Carpentaria, and Arnhem Land. The trough remained just off the north coast for most of the second week with Queensland seeing most of the monsoon activity. Shortly after mid-month the pressure gradient across the NT broadened out and there was very little activity across the NT. A few rainfall events affected the north coast, but rainfall totals during this time of the month were relatively small. Around the 21st of the month a surface trough moved into the southern NT. It lingered around the Alice Springs District before pushing north. Some places in the Alice and the VRD, including Rabbit Flat, saw some significant rainfall totals from this trough and a burst of cool southerly air briefly gave Top Enders a taste of dry season conditions. The trough had dissipated by the 26th and a ridge centered over SA pushed into the southern NT. Hot, humid, "build-up" conditions persisted across the Top End for the remainder of the month. page 2 Monthly Weather Review Northern Territory April 2013 Daily mean sea level pressure analyses 1 April 2013 2 April 2013 3 April 2013 4 April 2013 5 April 2013 6 April 2013 7 April 2013 8 April 2013 9 April 2013 10 April 2013 11 April 2013 12 April 2013 13 April 2013 14 April 2013 15 April 2013 16 April 2013 17 April 2013 18 April 2013 page 3 Monthly Weather Review Northern Territory April 2013 19 April 2013 20 April 2013 21 April 2013 22 April 2013 23 April 2013 24 April 2013 25 April 2013 26 April 2013 27 April 2013 28 April 2013 29 April 2013 30 April 2013 page 4 Monthly Weather Review Northern Territory April 2013 Temperatures The area averaged mean temperature (maximum and minimum temperatures combined) for the Northern Territory was 18.3 °C, 0.4 °C above the long term norm and the warmest April since 2010.