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graphs      CLIMATE-UK.COM'S  REVIEW  OF  THE  BRITISH  METEOROLOGICAL  SCENE
     MONTHLY  SUMMARY
     No. 609 For   SEPTEMBER  2006
EQUAL WARMEST SEPTEMBER IN 340 YEARS OF RECORDS                            EQUAL  WARMEST  SEPTEMBER  IN  340  YEARS  OF  RECORDS
Text Box: Once again a major change of type was synchronised almost exactly with the calendar: August’s northwesterlies gave way to southerlies in September resulting in persistently high temperatures throughout the month. This was the fourth most ‘southerly’ September over the British Isles, after 1901, 1903 and 1934. Mean sea-level pressure ranged from 2mbar below normal in Shetland to 9mbar below in western Ireland, and the main anomaly centre of -13mbar lay near 52N 19W.

A moist SW-ly flow covered the country during the first three days, bringing strong winds and much cloud, and heavy orographic rainfall affected western upslopes: Capel Curig collected 47mm on the 2nd, part of a 7-day (30 Aug-5 Sep) total there of 184mm. It was quite warm in eastern England especially at night and the minimum overnight 2nd/3rd at St James’s Park (London) was 18.9°C. The period 4th-11th was largely anti-cyclonic; highest pressure lay over France at first, and moist southwesterly winds delivered more rain to northwestern regions including a fall of 53mm at Tyndrum (Perth-shire) on the 5th, but temperatures climbed to 25-27°C in the south and east. Highest pressure transferred briefly to the west of Ireland on the 7th allowing a short-lived northerly incursion which resulted in a couple of cold nights, the mercury slumping to -0.8°C at Braemar (Aberdeenshire) early on the 8th. However, the anticyclone moved steadily eastwards over the next few days and a sluggish southerly airflow sent temper-atures soaring to 25°C or more from 9th-14th and peaking at 30.2°C at Heathrow (London) on the 11th, the highest September reading in the UK since 1999. Between the 6th and 12th, the sun shone for a total of 60-70 hours in many southern, central and eastern districts, and Kinloss (Moray) logged the largest daily total of 12.5 hours on the 8th.

Britain lay under a humid southerly flow from the 12th-21st, with high pressure still anchored over eastern Europe, while low pressure lay to the west of Ireland. Although temperatures were lower than hitherto, it remained rather warm especially at night (although an isolated cold night in Northern Ireland brought a reading of -0.1°C at Text Box: Katesbridge, County Down, early on the 16th). Heavy rain and thunderstorms broke out widely between the 12th and 14th, but eastern districts became mostly dry again for several days. However, it was very wet between the 18th and 20th in western regions, and Tyndrum collected 131mm of rain in 72h, 67mm of which fell on the 20th alone. On the 21st much of the country was spectacularly sunny and very warm, and the maximum of 29.0°C at Sutton Bonington (Notts) was the highest this late in the year since 1985. A small but intense depression, associated with the remains of hurricane ‘Gordon’ brought rain and rough winds to western parts of the UK overnight 21st/22nd with gusts to 69kn at South Uist (Western Isles); there were widespread power failures that night in Northern Ireland.

The rest of the month was cyclonic with lowest pressure over or just to the west of the British Isles. Showers broke out widely on most days, there were some torrential downpours, and thunder was frequently heard. Most places remained rather warm, but at Dalwhinnie (Inverness-shire) the day’s high on the 24th was just 12.4°C. An unconfirmed fall of 110mm at Gorleston (Norfolk) was associated with serious flooding in Gt Yarmouth and Lowestoft on the 25th. South Uist logged a gust of 64kn on the 27th during the passage of former hurricane ‘Helene’.

Mean temperature ranged from 2.0-2.5degC above normal in northern and western Scotland and Northern Ireland, to 3.0-3.5degC above in the Midlands, East Anglia and southeast England. Over a large part of the UK it was warmer by a substantial margin than any September in the last 100 years. Rainfall was much below normal in parts of southwest England where Portland (Dorset) received only 17mm, but much above in western and central Scotland and in parts of East Anglia. Sunshine totals were up to 25% above normal in central and eastern parts of both England and Scotland, but there was a large deficit in Shetland; totals ranged from 198h at Herne Bay (Kent) to 47h at Lerwick (Shetland).
                                                                                                                                           
                       TEMPERATURE                                SUNSHINE                             RAINFALL        
                                                                                                                                 
                                                                                                                                   
                                          Highest and lowest totals                     Highest and lowest totals        
                                              on record for month    
Maximum fall in 24 hrs
   (beginning 09 h)
                    on record for month    
Days with snow or sleet
 
Days with fog
(Vis <220 yards at 09 h)
 
                                                                                         
     
Difference from average
   
Difference from average
 
Highest maximum
   
Lowest minimum
   
No. of days with grass
  minimum below 0ºC
   
Days of no sunshine
 
Maximum duration
       
First year of record
         
Days of no rainfall
 (0.1 mm or less)
         
First year of record
         
Days with thunder
     
       PLACE  
Mean Maximum
   
Mean minimum
             
No. of air frosts
       
Total for month
                   
Total for month
                   
                               
% of average
                   
% of average
                 
                                                                     
                                   
Highest
   
Lowest
 
Year
             
Highest
   
Lowest
 
Year
       
             
Date
   
Date
         
Date
         
Year
         
Date
         
Year
           
                                                                     
      ºC       ºC       ºC       ºC             Hrs       Hrs         Hrs       Hrs       mm       mm         mm     mm          
                                                                                                                                           
  *Hampstead   22.2   +4.0   14.1   +3.7   29.4   11   08.8   08   00   00   01   09.2   10   147   110   1910   224   1959   072   1945   17   17.5   28   087   141   1910   157   1918   02   1959   02   00   00  
  Thorney Island   21.3   +2.1   14.4   +3.4   25.8   21   07.1   08   00   00   03   10.6   08   195   113   1958   245   1959   129   1967   13   19.0   22   067   125   1941   159   1974   02   1971   02   00   00  
  *Wattisham   21.3   +3.2   13.5   +4.0   25.8   06   06.9   08   00   00   01   11.9   10   155   108   1968   232   2003   103   1984   15   24.2   13   081   174   1960   119   1968   01   1969   04   00   00  
  *Wittering   21.7   +4.0   13.1   +3.4   28.9   11   06.0   08   00   00   01   10.5   08   157   111   1950   207   1964   093   1967   13   10.8   22   039   081   1948   132   1992   02   1959   04   00   00  
                                                                     
  Lyneham   20.6   +3.1   12.8   +3.2   27.3   11   07.2   08   00   00   03   12.2   07   160   111   1952   235   1959   100   1983   13   18.6   29   074   112   1945   142   1974   05   1959   05   00   00  
  Ross-on-Wye   21.4   +3.5   12.6   +2.9   27.0   11   06.0   08   00   00   01   11.3   10   161   124   1914   205   1929   069   1945   18   10.4   14   035   055   1859   203   1976   02   1865   04   00   00  
  *St Athan   20.6   +3.2   13.5   +2.8   24.5   10   09.5   16   00   00   01   11.9   08   142   097   1954   249   1959   074   1956   17   17.6   30   057   064   1954   223   1974   14   1959   01   00   00  
  St Mawgan   19.3   +2.2   14.0   +2.6   22.9   21   10.9   15   00   00   02   11.5   07   163   102   1945   258   1959   080   1956   16   18.8   28   044   055   1944   179   1974   10   1959   01   00   00  
                                                                     
  *Edgbaston   20.5   +4.0   13.1   +3.6   26.5   21   08.0   08   00   00   01   09.6   08   141   109   1887   216   1895   067   1909   17   18.0   13   077   134   1887   165   1918   04   1959   04   00   00  
  *Valley   18.7   +1.9   13.7   +2.5   25.5   21   08.0   15   00   00   01   11.9   08   155   109   1946   214   1949   096   1948   09   14.2   04   077   092   1941   174   1950   03   1986   01   00   00  
  *Woodford   20.1   +3.3   12.0   +2.8   27.0   21   04.1   08   00   00   00   11.4   10   143   115   1945   197   1959   069   1948   14   19.8   13   082   108   1942   171   1965   05   1959   02   00   00  
  *Watnall   20.8   +3.1   12.8   +3.1   28.3   21   07.4   08   00   00   00   11.0   08   141   100   1948   177   1991   075   1993   13   11.0   22   051   107   1942   147   1957   02   1959   04   00   00  
                                                                     
  *Leeming   20.5   +3.2   12.0   +2.8   27.5   21   04.2   08   00   00   01   12.2   08   134   110   1945   200   1986   073   1976   13   19.4   14   060   122   1945   174   1976   04   1959   04   00   00  
  *Boulmer   18.2   +1.9   11.7   +2.4   22.1   12   06.1   09   00   00   04   11.8   08   146   114   1945   205   1986   075   2001   11   22.8   02   062   112   1945   147   1965   12   2004   00   00   01  
  *Eskdalemuir   17.4   +2.5   10.0   +2.9   24.1   21   02.0   08   02   00   05   11.0   09   095   095   1911   153   1959   055   1980   09   31.2   20   181   127   1911   308   1950   18   1972   01   00   00  
  *Bishopton   18.0   +1.7   11.0   +2.3   23.5   21   05.1   08   00   00   05   11.1   08   085   074   1921   169   1996   068   1965   06   29.6   19   178   186   1921   258   1985   11   1972   01   00   00  
                                                                     
  *Leuchars   18.5   +2.3   11.0   +2.3   23.6   21   04.6   09   02   00   04   11.9   08   130   101   1922   181   1997   077   1956   13   22.0   14   090   174   1922   149   1950   05   1972   00   00   00  
  *Dyce   18.2   +2.7   10.8   +2.8   22.8   12   04.1   09   03   00   04   11.8   08   123   105   1941   181   2004   070   1968   12   13.4   05   043   067   1941   234   1995   15   1959   00   00   00  
  *Stornoway   17.0   +2.8   11.9   +3.2   20.1   22   07.5   30   00   00   04   09.4   30   090   083   1880   175   1903   070   1965   06   18.2   24   087   084   1943   206   1981   34   1968   00   00   00  
  *Aldergrove   17.9   +1.8   11.6   +2.2   21.3   05   04.1   08   00   00   02   11.7   16   097   089   1927   177   1986   070   1962   10   35.2   20   092   114   1927   163   1981   06   1986   00   00   00  
                                                                     
                                                                                                                                           
  Stations marked with an asterisk record sunshine electronically; comparisons      
  with earlier records are therefore somewhat speculative. Thorney Island's      
  sunshine figures are made at a nearby site.