Bobgram Tahiti to Tonga

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 24 May 2026 Tahiti to Tonga Now that many yachts are about to travel west from Tahiti to Tonga, it is time to review the weather, in general terms, for this route. The main players: 1. Getting from the Tahiti area to Tonga/Fiji means crossing the South Pacific Convergence zone, SPCZ. Like a dragon, it dances . This zone may be weak or may contain squally showers. In the models it is portrayed as a zone of light winds. To see a forecast for this zone, use windy.com and rain accumulation for a period over five days. This zone may linger in the north (it does this in an El Nino) or it usually hovers between Samoa and Southern cooks. To avoid it, choose a different latitude or aim for gaps in the zone. The SPCZ goes thru periods of activity and inactivity and is most active when there is the positive phase of an MJO (Madden Julian Oscillation). Occasionally a tropical low/passing trough will travel east/southeast along the zone, making for a burst of wind/rain travelling east from Fiji to Niue then SE across Southern cooks. These occur on occasions even at this time of the year and can be forecast beforehand and avoided. 2. Another thing to avoid is a SQUASH ZONE when a large High travels east along 30S. When the central pressure in the High is 1030hpa or above, it gets dirty (isobars get bunched together along its rim). So in the tropics the isobars marking the trade winds may get squashed together making a "squash zone" of enhanced winds and rough seas. These usually occur around 20 to 25 South and may last for several days. In Fiji this is called BOGIWALU, in Tonga AHO VALO, and in Tahiti the name used is MARA'AMU. They are reasonably easy to forecast and are worth avoiding. If caught in one, change your latitude rather than your longitude. Bogiwalu sweeps through palm leaves and pandanus; Salt spray and rain drive inland from the seas; Young August shields her face and droops her banners. And strips for flight, and with the wind she flees. July would fain forego her glorious gift of sunshine To breast a portion of the eight nights' strain. July's apparel-not for pain but peace time- Is armour poor against the wind and rain. Oh! linger not, July-with heart-warm kiss of sweetness: Go now-your golden sun-robe scarcely tom. Young August, swift and slim for greater fleetness, Plies through the years, and onward we are borne. V. M. P. COSTER. Suva Point, Fiji, 29/7/1939. (taken from PIM online) 3. The third thing to avoid is the PASSING TROUGH or passing low. The systems tend to form on the eastern end of the SPCZ in which case they travel southeast, propelled by upper NW winds as a steering field. OR they may form on the NW (back) corner of a travelling HIGH., in which case they may get shunted south or sometime to the southwest. They often have their own mini-squash zones (on their polar/southern side), and calm zones (on their equatorial/northern side). Isobars give a clue about the intensity of a passing trough: those above 1010hP are usually weak and those below 1007 are worth avoiding. There are three routes between Tahiti and Tonga, the northern, central and southern: 1. Sometimes the northern route via Suwarrow/Samoa is favored, and sometimes not. The northern route goes via Suwarrow to Samoa. Often this is covered by the SPCZ, but when the SPCZ is further south the northern route and its northeast winds may be best. 2. The middle-route offers stopovers such a Palmerston Island and Niue and is a good alternative when the SPCZ is further north. Watch out for passing troughs and squash zones . these come and go. The middle route allows short hops. 3. The southern route tends to get higher swells from the Southern Ocean SO, all in all, the "best voyage" changes every few days . sometimes it's worth waiting for something that suits, sometimes it isn't. Basically, avoid passing troughs and squash zones, and go thru the SPCZ where/when it is weak. This may mean taking short hops rather than getting direct from Tahiti to Tonga in one go. =-=-=-=-=-=-=-=-=-=-=- TROPICS No named storms at present WEATHER ZONES LOWS and HIGHS LowL1 over the Austral's tonight is finally expected to move off to the southeast after a week of travelling due eats. Low L2 has formed on western side of a cold pool aloft and thus been tracking to the NE . It is expected to weaken over Fiji and Tonga next few days but have lots of lightning in its squall clouds (over eastern Fiji and Tonga tonight). It is expected to travel ESE towards the Austral's this week, following L1. High Hi is quasi stationary over New Zealand. After a SW change along the east coast on Wednesday, it should be replaced by High H2 from Australia. Low L3 is forming under a cold pool over central Australia, so its rain clouds may be intense. Its wind and rain are expected to form a deepening low near Lord Howe by Friday which is expected to bring intense wind and rain from Fiji to New Zealand by Sunday (and that's the middle of a long weekend in New Zealand). Avoid. Rain accumulation from windy.com shows a rather weak and unorganised SPCZ. Also well-defined areas of rain associated with L1, L2 and L3. Parts of Australia have had their wettest May on record, and L3 takes another crack at Sydney. Wind accumulation this week from Windy.com shows a squash zone just north of NZ as part of L2 and the winds associated with L1 mainly about the Austral Islands, and winds from L3 spreading across the Tasman Sea with the approach of the Kings Birthday long weekend. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 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. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>