HF Communications Warning

(last updated 16 May 2025 23:45 UT)

SUBJ: ASWFC HF RADIO COMMUNICATIONS WARNING 25/48 ISSUED AT 2259UT/16 MAY 2025 BY THE AUSTRALIAN SPACE WEATHER FORECASTING CENTRE. HF conditions in the Australian region are experiencing depressions during local night hours which are expected to continue over 17-19 May. DEGRADED HF PROPAGATION CONDITIONS EXPECTED FROM 17-19 MAY 2025 IF COMMS DIFFICULTIES EXPERIENCED TRY A LOWER FREQUENCY BAND _____________________________________________________________ HF COMMUNICATIONS FORECAST (AUSTRALIAN/NEW ZEALAND REGION) FREQUENCY BANDS T-index MUFs 2 4 6 8 12 16 22 26 _____________________________________________________________ 17 May: 90 normal/-15% 2 4 6 8 12 12 16 22 18 May: 90 normal/-15% 2 4 6 8 12 12 16 22 19 May: 90 normal/-15% 2 4 6 8 12 12 16 22 Note: An ASWFC MUF depression HF Warning and ASWFC shortwave fadeout HF Warning are both current. Shortwave fadeouts degrade lower shortwave radio frequencies first (through increased ionospheric absorption) and the usual strategy during shortwave fadeouts is to try a higher frequency. In contrast, during periods of ionospheric MUF depression, the upper frequencies are degraded first and the usual strategy is to use a lower frequency. In general use a lower frequency if you are having trouble with your normal workable frequency. If a shortwave fadeout occurs during a period when ionospheric MUFs are depressed the available HF bandwidth will be "squeezed", with increased absorption raising the lowest usable frequency and the ionospheric depression lowering the highest usable frequency. Under such conditions it is suggested that the HF communicator operates on the highest usable frequency, even though this may well be in fact lower than what is normally supported for that particular circuit.

Please note this icon refers to any current HF Depression Warning. For HF Fadeout Warnings, see here.