Bobgram

Bob McDavitt's ideas for sailing around the South Pacific. Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world. Compiled 19 July 2026 Anticyclonic gloom You have probably heard all about the High-Pressure heat domes giving high temperatures over Europe this summer. And you may have puzzled about the low grey clouds found over the ocean in the high-pressure regions of the South Pacific, especially in winter. These High-pressure regions are three-dimensional. In the vertical the top part of the system contains sinking air. Just as rising air cools, so it is that sinking air warms. But the sinking air doesn't go all the way down to the surface. Instead, the bottom layer hugging the ground gets trapped ---it contains moist-laden marine air with flat grey clouds, mist and maybe fog, smog and polluted air. Anticyclonic gloom-a trapped layer of marine-moistened air. There is a distinct layer separating the warmed air aloft from the bottom trapped layer. Between the sinking warmed air and the trapped layer is a thin interface --- a lid called a subsidence inversion. It is formed by subsiding air and it inverts the normal rate of change of temperature with height. Key Characteristics . Stagnant Air: Light winds inside the high-pressure system fail to push the clouds away, meaning the gloom can linger for days . Temperature Inversion: Warm, sinking air sits above cooler, moist marine air, firmly trapping the cloud layer below . Mild & Drizzly: Despite the grey skies, temperatures usually remain mild. The moisture in the marine layer can occasionally condense into dense fog or light drizzle. The Science Behind the Gloom The mechanics rely heavily on atmospheric physics: 1. Subsidence: Descending air within an anticyclone compresses and warms, forming a stable "lid" or inversion layer. 2. Moisture Trapping: The cool ocean waters keep the lowest level of air moist. Under the lid the air is blocked by the warm air above it, so the moisture spreads out into a blanket of stratus or stratocumulus clouds. 3. Lack of Wind: Without significant wind to mix the atmosphere or break up the cloud deck, the overcast, gloomy conditions remain stationary. TROPICS . After devastating the Northern Mariana Islands, a weaker Bavi crossed the western Pacific and inundated parts of China's Zhejiang province. WEATHER ZONES The South Pacific Convergence zone remains well north of its usual position. And now it has curled around itself on its western side and produced a tropical low. I wonder if this is in response to the strong east-going current at the equator.? Here is MetService streamline analysis, showing a rotating feature very close to the equator (physically impossible to happen AT the equator) . Interesting to see a triplet of lows so close together they almost share the same streamline, with two going clockwise and the third counterclockwise. That doesn't happen often. I've named that feature L2 and it is expected to drift south into an area of strong shear and unwind near northern Vanuatu. Low L1 formed recently near New Caledonia and is expected to travel east along 20 to 30S crossing Minerva on Tuesday night, and followed by some high South to southeast swells. Avoid. After a quick front crossed North Island on Monday, High H1 should travel along 40S across Tasman Sea and NZ, very likely with some anticyclonic gloom. It then may fade but extend a nose to the northeast, weakening the trade winds between Tahiti and Tonga. Typical El Nino. From Friday a series of fronts and strong disturbed westerly winds, all on north side of L3, are expected across the Tasman Sea/NZ area. Typical El Nino. So, after several weeks with stalling systems, the weather this week transits into a mobile pattern. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> If you would like more details about your voyage, check metbob.com Or Facebook at /www.facebook.com/metbobnz/ Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom). Weathergram archive (with translator) is at weathergram.blogspot.co.nz. Contact is bob@metbob.com or text 64277762212. >>>>>>>>>>>>>>>>