TONGA TO NEW ZEALAND – CHAMELEON’S IDEAS –IF SHE FEELS LUCKY!
David Sapiane BSc Gulf Harbour Radio
SOME GIVENS:
New Zealand (NZ) longitude ~ 172 East
Tasmania (TAS) longitude ~ 147 East
Brisbane (BRIS) longitude ~ 153 East
Average yacht speed 6.25 knots
SOME AVERAGES:
FEATURE SPEED DEGREES/DAY TAS TO NZ BRIS TO NZ
Cold Front 20-25 kts 8-10 2-3 days 2-2.5 days
Fast Cold Front 40 kts 16 1.5 days 1.2 days
High Center 15 kts 6 4 days 3.3 days
Low Center 25 kts 10 2.5 days 2 days
LEAVING TONGA FOR NZ WITH WAYPOINT ABOUT 28S &173E
1. Leave Tonga as a High Center is at longitude of NZ. If averages prevail the next Low should arrive in NZ when we arrive at about 28S.
2. Arriving at about 28S as a Low crosses Northland we may have 4 days before the next one.
3. Leaving Tonga as a cold front crosses Northland may look good for winds at the start but may also allow us to unforgettably greet the next front as we’re closing with NZ.
LEAVING TONGA FOR MINERVA, THEN TO NZ.
1. Distance to say Auckland from Minerva is about 840 nautical miles or 5.6 days. This stop shortens the distance to NZ and allows for more accurate analysis.
2. Consider leaving Minerva when a cold front crosses NZ and the new High is about the longitude of Tasmania.
3. We may strike a bit of the front as we head south with a period of adverse wind.
4. If we’re lucky we’ll arrive in NZ as the new High embraces the country.
KEEP IN MIND
1. If a Low center is at the longitude of Tasmania the SW wind change over NZ can occur in about 3 days or sooner.
2. Some Lows can spawn multiple troughs after the initial cold front.
3. New Lows can spawn very quickly in the cold air just behind an existing Low. These can surprise forecasters.
4. Lows and Highs can, and usually do, change shape, size, and speed. This fact will skew the averages and ideas put forth above. This is also why we always use the “gribs” (GFS Model) to make our final decisions. The model may not always be accurate but it’s better than guessing.
5. If we make a plan we stick to it. If this involves using the engine to maintain target speed, we do it. We have run into trouble by wasting time wallowing in light air.
6. The ideas change if the yacht speed differs from 6.25. The math is simple if you want to recalculate for a different speed.
7. None of the above is advice nor should be taken as such.