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.