Effective as of 4:00 AM Thursday September 24 2020
Explanatory notes:Strong easterly winds in the morning with a strong high pressure system to the south and a low forming to the northwest ahead of an upper level trough.Middle level clouds and possible elevated convection from afternoon ahead of an upper level trough with cold air in the middle levels and warm air in the low levels. However, there will be plenty of dry air below the 650 hPa level until some more moist air to the northwest later at night and this could inhibit elevated shower and thunderstorm development.
Gusts to 90 km/h possible over the hills and foothills on Thursday night and early on Friday should strong winds aloft mix down with ECMWF model showing winds up to 90 km/h at the 950 hPa level under a weak inversion.Precipitation/virga can also push these strong winds down. Easterlies of this intensity are rare for this time of the year.
Showers possible on Friday with the low to the southwest and moist air making its way in the lower levels, also possible thunderstorms, most likely during the early hours with the cold air still aloft.
On Saturday, showers and also possible thunderstorms depending on the position of an upper level disturbance.
Showers possible for the rest of the forecast period from Sunday with a moist westerly flow.
Thursday September 24:
City:
13-30 Degrees Celsius
Partly cloudy.
Chance of any rain:10%
Amount:Nil
Perth Metropolitan Area:
Partly cloudy.The slight chance of a shower or thunderstorm from afternoon.Winds easterly at 20-40 km/h. Gusty winds possible about the hills and foothills early and again at night, gusts possibly reaching 90 km/h over the hills and foothills later at night.
Friday September 25:
City:
14-24 Degrees Celsius
Shower or two.Possible early thunderstorm.
Chance of any rain:50%
Amount:0 to 2 mm
Perth Metropolitan Area:
Partly to mostly cloudy.A medium(50%) chance of showers.The chance of a thunderstorm most likely early.Winds east-northeasterly at 25-40 km/h easing to 15-25 km/h in the morning shifting northwesterly around the middle of the day.Gusts up to 90 km/h possible over the hills and foothills early.
Saturday September 26:
City:
12-21 Degrees Celsius
Showers.Possible thunderstorm.
Chance of any rain:90%
Amount:2 to 8 mm
Perth Metropolitan Area:
Partly to mostly cloudy.A very high(90%) chance of showers.The chance of a thunderstorm.Light winds tending west-northwesterly at 15-25 km/h during the day.
Sunday September 27:
City:
11-21 Degrees Celsius
Shower or two.
Chance of any rain:60%
Amount:0 to 2 mm
Perth Metropolitan Area:
Partly to mostly cloudy.A medium(60%) chance of showers.Light winds tending west-northwesterly at 15-25 km/h during the day.
Monday September 28:
City:
11-20 Degrees Celsius
Showers.
Chance of any rain:80%
Amount:2 to 8 mm
Perth Metropolitan Area:
Partly to mostly cloudy.A high(80%) chance of showers.The chance of a thunderstorm.Winds west-northwesterly at 20-30 km/h.
Tuesday September 29:
City:
11-20 Degrees Celsius
Shower or two.
Chance of any rain:60%
Amount:0 to 1 mm
Perth Metropolitan Area:
Partly to mostly cloudy.A medium(60%) chance of showers.Winds westerly at 15-25 km/h.
Wednesday September 30:
City:
13-20 Degrees Celsius
Possible shower or two.
Chance of any rain:40%
Amount:0 to 1 mm
Perth Metropolitan Area:
Partly to mostly cloudy.A medium(40%) chance of showers.Winds westerly at 15-25 km/h.
Charts:
Figure 1.Surface synoptic chart at 12 UTC(8 PM local time yesterday).Image courtesy of the Australian Bureau of Meteorology(BOM).
Figure 2.Key features identified on True Colour RGB satellite image at around 06:00 UTC(2 PM local time yesterday).Satellite image courtesy of the Japanese Meteorological Agency(JMA).
local time yesterday).Image courtesy of the Australian Bureau of Meteorology(BOM).
Figure 4:Surface synoptic prognosis.Image courtesy of the Australian Bureau of Meteorology(BOM).
