Modern weather-analysis consumers are familiar with the term "atmospheric river", describing a multi-year-cyclic weather phenomenon, a key element of climatological mechanics, in which water is evaporated from oceans in warm locales, then moved long distances to fall as heavy rain. In "El Nino" periods, a Pacific atmospheric river dumps rain on the southwestern and central-southern USA. Much of that water originates north of Papua New Guinea, in a band from the northwest extending eastward.
Warm high-evaporation oceanic regions like this have measurably higher surface salinity, which can be determined via satellite measurement of infrared emission characteristics. This is a recent salinity map for the Pacific Ocean. Red areas are higher salinity because of lower rainfall and high sunlight evaporation, blue ones are where it rains a lot and surface salinity is lower:
USA isn't the only place affected by the "atmospheric river" phenomenon. Currently Australia has two...one affecting western Australia, originating in the Indian Ocean, and not of immediate interest to this thread, and the other affecting eastern Australia, and of direct interest. That second "atmospheric river" has been estimated to have a water flow rate of about 600 Murray Rivers. Murray River is the longest river in Australia, and is pretty good sized, so that's a lot of water. Most of the evaporated warm water from north of PNG, and the immense amount of thermal energy it contains, flows eastward into the Coral Sea. Some continues across the Pacific to be a dominant factor in the weather of much of North America, but the rest feeds a circulation path that rotates around PNG, and...normally...sends massive air-water-and-energy flows through the valleys of the Owen Stanleys. That's the driver for the daily thunderstorms and frequent rain squalls around the peaks and up and down the valleys.
Note the deep blue along much of the southern coast of PNG. The same infrared methods cannot measure rainfall on land, but the rain rates in the Owen Stanleys are
*much higher* than over the sea, as the massive amount of warm water in the airflow collides with the mountains and generates thunderstorms.
Right now, there's a low pressure zone over central Australia, stuck there because a high pressure zone in front of it is stalled. That's causing a sizeable part of the southern fork of the "atmospheric river" from the Coral Sea that normally circulates westward around, and then northward across PNG to be attracted to that low, and wrap clockwise around it as it bends far to the south, and drop massive amounts of rain over eastern Australia.
My understanding is that during the WWII years, weather patterns across the Coral Sea and the land to its west...PNG...were more conventional. The warm water north of PNG, indirectly and circuitously, drove the atrocious wet weather in the Owen Stanleys via moisture and thermal energy wrapping back from the Coral Sea, and eastern Australia had moderate, temperate weather.