What's up with the weather?

I made it to Kerikeri today and am resigned to waiting until this @&($&/ weather system passes before I can proceed onto Norfolk Island.  There's about a 10% chance I might be able to proceed on Sunday but it's more likely that Monday will be the day.

So what is up with the weather? As I have time on my hands at the moment I thought I'd record the resources  I'm using to evaluate the weather and decide whether it's suitable for flight. These are a little different from those used prior to a Sunday afternoon flight somewhere for a coffee.

General situation/synopsis

First a check is made of the 5 day rain forecast published by the Met Service to gain a general appreciation of the weather systems that will impact my route.  This forecast shows both wind and rainfall so you can begin to visualise the weather that will be encountered.

Although the graphics aren't as clear I find the Met Service forecast better than the popular Metvuw. The Met Service seems more accurate and takes better account of the New Zealand geography when plotting the wind.

At the moment the general situation shows a large high pressure zone to the south of New Zealand which is barely moving. That's preventing a low from moving East or South and out of the way of my track from New Zealand to Australia. The winds rotate clockwise around a low and so that is dragging warm moist air down from the tropics leading to low cloud and showers.

Terminal Area Forecast (TAF)

Next thing to check is the TAF for your destination and any airports you might pass on your route.  The TAF provides a local forecast for the 10 mile area centred upon an airfield.  TAFs are available from the Australian NAIPS service (their equivalent of IFIS/MetFlight) and also the 

Australian Bureau of Meterology (a fantastic weather resource).

For this trip the TAF of Norfolk and Lord Howe Islands is critically important. As I do not have the range to fly to another airport when reaching the islands I have to have absolute confidence the weather at the airfield is suitable for landing.

For my flying mates here's the TAF that was published for Norfolk Island (YSNF) and applicable to my arrival time.

TAF AMD YSNF 272319Z 2800/2818 35008KT 9999 -SHRA FEW005 BKN012

BECMG 2807/2809 02005KT 9999 -SHRA SCT004 BKN008

FM281200 02005KT 8000 -SHRA OVC005

TEMPO 2800/2812 4000 -SHRA BKN005

TEMPO 2812/2818 2000 -SHRA BKN003 RMK

For my non-flying mates the above TAF told me the general weather for the day at Norfolk Island included a light northerly wind, light showers and rain. The cloud base is 1200ft with patches of cloud at 500ft. However that cloud base was lowering to 500ft in light showers and rain between midday and midnight - the time I would be arriving. In addition the visibility of 4000m between midday and midnight is less than the legal minima for visual flight. In short I would be arriving over an Island shrouded in mist and rain (if I could find it) with no alternative but to conduct an illegal landing. Sorry - I'm not signing up to that.

Route forecast

If the destination weather is suitable I then turn my attention to the weather that's likely to be encountered on the route. I've signed up for a month to the New Zealand Met Service MetJet service. Although principally designed for the big boys that cruise in shirt sleeves with multiple engines at 35,000ft it does provide good forecasts at the altitudes that us "bottom dwellers" fly.

There are a number of charts available from MetJet that provide details of significant weather and winds. Today's SIGWX chart shows significant cloud and isolated thunderstorms on the route from Cape Reinga to Norfolk Island. :(

One thing that's important that MetJet provides is the winds that can be expected between each waypoint on the route and where the freezing level is:

The winds are important because if there is too much headwind I may not have the endurance to make my destination. If my average ground speed drops to 118kts my planned fuel would be exhausted and my 45min fuel reserve would start to be used.  I won't set off if I know that could happen.

Satellite images

Finally the visual and satellite images of the Tasman sea are checked. This supplements the forecasts and lets you know where on the route cloud is likely to be encountered. However, what is generally not known is at what height the base and tops of those clouds are. You have to hop in your plane and go and look to find that out in the Tasman.

METAR

Immediately prior to departing I check the METAR at the destination airfield.  METARS report the actual conditions at an airfield and are issued every 30 mins on Norfolk and Lord Howe Islands.  Aside from knowing what weather is at the airfield a check is made that the METAR is consistent with the forecast (TAF).

In flight I'm carrying a satellite phone and can call an Automated Weather Information Service (AWIS) at Norfolk and Lord Howe Island airports to check the actual conditions before proceeding past my calculated Point of No Return.

Congratulations if you've managed to read this far! For all the fantastic weather resources we have available today there is still one "random variable" - the pilot and his interpretation of the weather forecasts and reports. We're all inclined to read into the weather reports what we want to see sometimes. There's nobody there to tell you to "go" or "not go". You are ultimately responsible for that decision yourself.

If you are looking for perfect safety, you will do well to sit on a fence and watch the birds; but if you really wish to learn, you must mount a machine and become acquainted with its tricks by actual trial - Wilbur Wright.