Bad moon rising?

Perigee is the name astronomers give to the closest earth-moon distance for the month. On 6 May it is the May perigee. It will coincide with full moon. The moon will swing in 356,953 kms from earth, and will look extra-big and extra-bright as it rises at sunset. On the day of any full moon the moon rises above the horizon at the exact second that the sun disappears beyond the horizon, which in Auckland on 6 May will be 5.24pm.

And not only does this month's perigee coincide with full moon but this perigee will be the nearest to earth of any this year, as the distance of the moon's close approach varies and the apparent size varies by up to 20%. The last closest was 20 March 2011 and the next time it will be as close will be January 2014. This month's full moon is due to be about 17% brighter than average. In contrast, later this year on Nov. 29, the full moon will coincide with apogee, the moon's furthest distance from earth, which will be relatively smaller and dimmer.

There is always reason to be careful around all perigees, as they exaggerate whatever else is going on in weather. Closest perigees are even more reason to be vigilant. Last year's closest perigee in March brought the Japanese tsunami earthquake and a 7-intensity earthquake in Christchurch. As usual, the normal seatides around the world will be particularly high and low. This is because at perigee, the moon exerts over 40% more tidal force than during its next apogee two weeks later. Kingtides are primarily kingtides in the land, and large earthquakes occur with double the frequency in the week of perigee. Closer perigees increase that seismic risk. Sea mammals have already started beaching in Peru which portends earthquake activity in that region. Perigees bring high winds because the extra gravitational pull on the atmosphere created by the moon's proximity creates turbulence.

What weather will ensue around the world? In Australia the only rain is expected along the North, Central and South Coast of QLD and along the south coast of WA, also the North Coast of NT, the extremities of the continent. Some extreme heat is likely in SA and heavy frosts in the Southern Tablelands. Gales are expected in Tasmania and a cyclone is likely to form in WA's northwest. A few days after the perigee snow should arrive in Tasmania and Brisbane should get thunderstorms. Ireland is expected to be rainfree on the 6th-10th but wet 1st-5th. The USA can expect rain and snow in the western States and rain with thunderstorms in the east, with winds generated by the perigee a possible hazard. In the UK, this May should be unusually cold for northern Yorkshire northwards. It is on a par with 2003, all things lunar being on a 9-year turnabout, and before that, 1993. Those were all record cold May months. This month's relatively closer perigee is the key. Expect the last week of May to be the coolest, especially for Scotland and north Wales, being the period of new moon in northern declination. 

When full moon and perigee occur together on the same day, the few days on either side is usually dry and on either side of the 6th this should be the case for most of NZ.  Here in NZ the likelihood is of heavy frosts due to the moon's southernmost position occurring two days after perigee. In some places it will resemble snow. However significant and widespread snow is not expected in NZ until the last week in May.

The higher tides also bring risk of seismic activity again to NZ, with potent dates 5th and 11th. The kingtides span 6th-9th and the concurrence of significant planetary alignments that include Sun Venus and Mercury should produce extra susnpot activity which incurs earthquakes. Watch for the barometer to sharply rise for that is an indicator of pressure release imminent in the ground. With the North Island already starting to twitch, May could be an active month for shakes, with the need to be watchful around 5th, 11th, 15th-18th, 20th-21st, and 27th-30th.

Of course none of these may happen, but the potential is there. Longrange predictions are nothing more than warnings due to potentials, and it is up to the reader to take note or ignore. The reason we have metservices is for these warnings to be issued, based on patterns that have occurred before. At the very least boats should be secured or brought to sheltered havens during the perigee, because coastal gales and higher tides have a habit of breaking moorings.

As for the rest of May in NZ, just about everyone should have a drier than normal and what could turn out to be about the third or fourth driest month of the year. Perhaps only central Plateau, parts of Waikato and parts of the W and S of the SI may be wetter than average. There are chances of thunderstorms in the second and last weeks of May.  But from 5th-10th should be mainly dry for most districts. The SI may also be dry 14th-19th. That means in the second and third weeks only about 3 rain days are likely for the SI.  The NI could be mainly dry 3rd-12th, 15-18th, and 24-28^th.  All NZ regions may only have about 12 rain days each this month.

The full moon perigee tides last until July then change to new moon perigee tides by September. In NZ we will still have snowfall times this winter, and even some extreme weather, but this year these moon positions signal a mostly milder winter season overall as compared to recent winters.

For more information email ken@predictweather.com