Published 19 July 2023.
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A: Overview
1. Influences.
Changes in sea temperature
Sea temperature anomalies in most of the North Atlantic remain warmer than climatology for the middle of July. Areas around the UK, western Europe, western Mediterranean and the Baltic show 1 to 3 Celsius anomalies with the Mediterranean area 3 to 5 Celsius above average.
Ocean anomalies along the equator show an established El Nino state. The extent of the cold anomaly to the west of North America has again increased in size a little.
(Error in June edition spell checker changed to Adriatic should read read Arabian Sea)
Atlantic Hurricane season 2023 has seen some tropical storm strength systems but not a full hurricane. (Wikipedia)
The Tropical Atlantic sea temperature anomalies are warmer than average having exceeded the forecast issued in June. Sea temperature in the tropical region are forecast to maintain positive anomalies through into Winter 23/24. (see Met Office graphic below).
Western Pacific and Indian Ocean tracks are shown below along with the time line.
According to Wikipedia Northern Indian Ocean storms have contributed to 480 fatalities and a cost of 1.5 Billion US dollars. Western Pacific storms have led to 11 fatalities and a cost of $137million although it is too early to assess the effects of the recent storm Talim which produced some damage and flooding in southern China.
Tropical Pacific Sea Surface Temperatures (Nino3.4) are in an El Nino state and forecast to remain so into 2024. This may result in a higher global average temperature for 2023 and 2024 and there are suggestions that over the next few years the global temperature average will set further new records.
The effects of the El-Nino may be difficult to predict due to the excessive heat in water around coastal western Europe.
The North Atlantic Oscillation index (500hPa index shown below) became negative in early July and are forecast to turn to neutral state over the next few weeks. Affects on the UK area are inconclusive for a neutral state.
See https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/north-atlantic-oscillation
2. Recent Climatology
See wiki pages with regards to heat waves:
https://en.wikipedia.org/wiki/2023_European_heat_waves
https://en.wikipedia.org/wiki/2023_heat_waves
In addition to a record breaking June there have been a lot of new all time temperatures records broken in July across parts of southern USA and Southern Europe as well as in Asia.
SW England
July to 17th 2023, has been cool than of late although temperatures have still been marginally above average. Rainfall has largely reached or exceeded the full month total and sunshine looks to be slightly below average to mid month.
UK:
Met Office provisional Temperature and Rainfall anomalies for 2023 April May June are shown below. Temperatures in most areas were above average. Rainfall was above average. in most places hence it is shocker that hosepipe bans are require although there has been climate data showing increased run off rather than retention of water in the soils.
Due to the ongoing rise in temperatures over the last 60 years, 30 year averages used for comparisons have increased hence what appears to be average as in April 2023 when using to 1991 to 2020 values would have been above average using the 1961 to 1990 values. Changes in rainfall are less clear cut but suggest slightly higher rainfall in the most recent 30 year average.
Copernicus, European sourced temperature and rainfall anomalies for June 2023 and the 12 months to the end of June compared with the 30 year period 1991-2020, are shown below:
UK River flows and ground water levels in June 2023 can be found in the Hydrological Summary
River flows across SW England were below average in June 2023. River flow data for the 14th July from the UK Water Resources Portal shows mostly above normal flows following the recent wet weather although North Devon and North Cornwall seem to have nearer normal flows
Reservoir levels, according to SW Water are approaching the long term average across SW England as of 16th July 2023. Despite this hosepipe bans remain in force across Cornwall and much of Devon.
The Global Flood Awareness System – GloFAS – forecast from July 1st to end of October 2023 shows a “normal” flood risk across SW England – does not cover flash flooding from for example thunderstorms.
B: Forecast data:
1. Stratosphere:
The polar vortex remains in summer mode as shown by the GFS 19/1200UTC analysis at 10hPa
2. Upper troposphere:
CFSv2 200hPa contours (top row) and CFSv2 anomaly (lower row) for August September October 2023.
3. Lower Troposphere:
A selection of model solutions for August to October 2023 using July data are shown below. The full set, including available graphics for Autumn 2023 can be found at https://www.weather-info.co.uk/wxsvc/seaslatest.html
Top row temperature anomaly. Lower row precipitation anomaly
August to October 2023
CFSv2 E3 data (below)
NMME data (below)
ECMWF (below)
NASA (below)
Data from WMO:
Three month average anomaly followed by August September October 2023. Top row temperature anomaly and lower row precipitation anomaly.
WMO super ensemble (below) is a mean of data supplied by National Meteorological organisations across the globe. Because of the amount of data the output is a low resolution. Note rainfall anomalies show marked cancellation between wetter and drier solutions in some of the multi model ensembles. Due to problems with the host web site WMO means are shown rather than the probability charts.
Individual members of the WMO super ensemble are shown below (Beijing China missing)
C: Comparing previous output:
April to June 2023 – based on March 2023 data.
Observed data.
Temperature: above average for season.
Rainfall: mostly below average for season although April was wetter in places and a few places may have been near average overall.
Sunshine: above average all of UK due to sunny June
Pressure: above average for season and each month
Original Summary – 190323 Temperature: for the three month period above average most likely. Most models suggest slighly larger anomalies for the second half of the period with a chance of near normal values early in the forecast period, perhaps more especially in the south. Rainfall: Overall near normal for the period. Some hints at above average early in period and below average later. Lots of uncertainty but slightly more models have drier rather than wetter June. Pressure: near normal with hint at above normal. Caution: 1: Large scale blocking with easterly types seem to only be forecastable about two weeks ahead.
Comment on summary: Good temperature forecast and trend through season, only fair for location of near average early in season.
Rainfall signal for drier June was good as was wetter start to season. Overall forecast of near normal less good. Indication for above average pressure was good.
Scoring will attempt to state good, fair, poor or no signal.
Revised order
1. Russia (WMO): Temp fair . PPN fair .
2. USA – CFS2 : Temp good . PPN fair .
3. UKMO Contingency: Temp good . PPN good .
4. UKMO : Temp good . PPN good . PMSL good
5. USA – IRI : Temp fair . PPN poor .
6. KMA APCC : Temp missing . PPN missing .
7. JMA : Temp good . PPN fair . PMSL good
8. NMME : Temp good . PPN fair .
9. WMO multi : Temp good . PPN poor .
10. BCC : Temp good . PPN poor .
11. NASA : Temp good . PPN poor .
12. CanSips : Temp fair . PPN fair .
13. Copernicus Temp fair . PPN fair . PMSL poor
14. CMCC Temp good . PPN fair . PMSL poor
15: DWD Temp good . PPN fair . PMSL poor
16. EC Temp good . PPN fair . PMSL fair
17 JMA Temp good . PPN fair . PMSL poor
18 UKMO Temp good . PPN fair . PMSL fair
19. MF Temp good . PPN fair . PMSL poor
20 NCEP Temp good . PPN fair . PMSL poor
21 ECCC Temp: good . PPN fair . PMSL poor
ECMWF mnthely graphics good signal for drier June but not widespread enough.
WMO low res data:
BoM Temp fair . PPN fair .
Can Temp fair . PPN poor .
DWD Temp fair . PPN fair .
KMA Temp good . PPN fair .
MOSC Temp poor . PPN poor .
WASH Temp good . PPN fair (good June signal) .
CMA Temp fair . PPN poor .
ECMWF Temp good . PPN fair .
UK Temp good . PPN fair .
JMA Temp good . PPN fair
MF Temp good . PPN fair .
CMCC Temp good . PPN fair .
CPTEC Temp fair . PPN poor.
D: Text Forecast for SW England
Remainder of Summer 2023 (August)
Temperature: Anomalies suggest around 1 deg C above normal, virtually all models above normal.
Rainfall: Highest probs are for near normal rainfall, suggestion of above normal for northern and western pasrts of the region.
August climate: 1981 to 2010 average daily mean temperature 16 or 17°C in main urban areas also locally east of the moors and more widely in Somerset, 13 to 15 Celsius elsewhere. Average 1981 to 2010 rain 40 to 80mm but over the moors, typically 125-150mm.
Autumn 2023 (September October November) limited data.
Temperature: A milder than average Autumn is most likely, consistent across models.
Rainfall: Probably wetter than average for the season. Month to month detail unreliable but hints at a drier start and wetter end to the season..
Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm. September often drier than October or November.
Winter (December 2023 January and February 2024) limited data
Milder than normal winter overall although December could see near normal temperatures. Rainfall average or above for the season but with a chance that December and / or February could see longer drier spells. Snow probably again below average so any accumulations more likely to be across the moors.
Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.
E: Caution.
Experimental Long Range Forecasts do not have a good success rate. especially with regards to precipitation. The models are good at predicting above average values but not for picking out a one off colder month. The data used for the above forecast summary can be seen at here.
The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary
F: References.
SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579
IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.
UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/
NMME information: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1
CFS2 info
GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.
‘Copernicus Products’ as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus http://climate.copernicus.eu
International seasonal monthly data from WMO
Climate data from The Met Office UK and NCEP USA
Contains public sector information licensed under the Open Government Licence v3.0.
t2mike 