St Helena – forecasting at one of the world’s most remote airports

St Helena is a long way from where you are – it’s a long way from anywhere. The nearest land (and diversion airfield) is Ascension Island 703 miles away and the mainland of Africa is at least 1200 miles away. Prior to the building of the airfield, it was also a long time from anywhere; a 2-3 day trip from Ascension Island or 5 days from Cape Town, both by ship, were the only ways most could travel to or from the Island.

St Helena Airport

St Helena Airport

The Airport opened over a year ago.  The Met Office provides weather services for the airfield and aircraft operators, through the work of an onsite Operational Meteorologist. The meteorologist has worked closely with partners in St Helena Government, ATNS, and Basil Read (the Airport Operator) to help establish how the weather impacts on flight planning and operations, then providing forecasts to help both. The location of the airfield means there is a potential for strong winds and wind shear to affect the airfield and approach. The risk of low cloud, poor visibility and ‘foggy showers’ all need to be considered too.

Remoteness equals challenging

The remoteness makes life on the Island very different to that back in the UK and also makes forecasting more challenging. Despite the installation of some Met Office technology on-Island to provide weather data and observations via satellite there are some limitations. For example, the computer model resolution is much less refined compared to over the UK and due to the isolation of the island there is a relative lack of local observations to help verify forecast data. Other than the soon to be retired RMS St Helena, the nearest regular downwind observations are made in continental Africa and passing traffic is very low, making aircraft and ship data rare.

Martin Hopwood, our resident meteorologist on St Helena, said

 “The building of local experience and the work of my predecessors, with support from multiple teams back in Met Office HQ, has been crucial. Over the time the Airport has been operational, and in the period leading up to the opening, data collection and analysis has taken place to consistently improve the knowledge base and work towards increasing understanding of the hazards and make the forecasting of them more accurate.”

So far, flights have included life saving medical evacuation to facilities not available on-Island, charter flights to bring essential staff to the Island, privately operated planes, as well as test and calibration flights. Every flight so far has been more of a ‘one-off’ whilst waiting for the regular flight operator to be chosen and put in place. Since Airlink was named as the provider of regular flights there needed to be another one-off flight, a proving flight on 21 August.

Airlink proving flights August 2017

Airlink Proving Flight, 21 August 2017

Planning inbound flights happens the day before an arrival

Outlook forecasts for the upcoming three days are issued daily by the airport meteorologist, and seven day outlooks are issued twice a week based on ensemble forecasting models. But these are not for planning purposes – the typical preparation for a flight begins the day before an arrival.

Martin explains a typical day:

“On arrivaI I review all the available model and observation data, and weather observations are made by the duty observer to enable production of a TAF, and any applicable weather warnings. I also put together a detailed wind forecast for three points on the runway as aircraft have the option of landing from the north and the south, and write a general weather situation for take-off and/or landing times. This, along with all the other daily tasks such as the collating and analysis of data, and maintaining the forecasts takes me through to 5pm, the time I leave the office and pass the forecasts to our team in Exeter for overnight support.”

The meteorologist here is often last out of the building and then first in the next morning. The early start is needed as flights mostly start in a territory that is 2 hours ahead and an 8 hour journey away (including one stop on the SW African coast). Forecasts need to be consulted by the aircrew before setting off. Arriving at 4am the meteorologist starts again by updating all forecasts for the day in light of new data that has come in overnight. Warnings for the airfield, approach and the upper air in the area surrounding St Helena are also provided as necessary, including an assessment of wind shear on approach.

St Helena is a Category C airfield on a remote island

These forecasts and warnings all need to be monitored and updated throughout the day and the meteorologist is constantly available to discuss the weather forecast with those who are looking to it to answer their questions. Martin has briefed pilots the day before, first thing in the morning and en-route, both on the ground and in the air to help them make those crucial decisions with the best possible advice.

St Helena is a Category C airfield on a very remote island.  Once an aircraft passes its point of no return, the options for diversion airfields are very limited should an aircraft not be able to land at St Helena Airport.  It is therefore key to make sure a pilot is aware of what weather conditions are possible at St Helena Airport so that the pilot can determine whether to proceed to St Helena or to turn back.

Support is also given to ground staff as sometimes visibility can drop sharply and quickly and winds can potentially reach hazardous speeds. Local staff need to know when they have the window to perform their duties on the runway and surrounding area safely and efficiently

The Met Office recently used a LiDAR to collate detailed measurements of wind flow over the threshold and approach areas of runway 20. This period of data gathering proved to be very successful, so much so that a permanent LIDAR is currently being installed adjacent to the runway. The data from the LiDAR will be used to develop an in depth knowledge of the wind flow that aircraft will experience on their approach to the island, ensuring the provision of the best possible forecast information. Additionally, real time data will be conveyed to aircrew during final the final approach of aircraft to the airport.

In the future the regular flights will far outnumber the one-off flights. Our experienced meteorologists along with the installation of a LiDAR at the airfield will accelerate both the knowledge gathering and the ability to provide crucial and quality forecasts for flights that are set to bring forth ‘the next step in St Helena’s history – one that will ultimately bring a better standard of living and a better future for everyone who lives here’. The proving flight was another example of things going very well from a forecasting perspective, the wind and the rest of the weather were as forecast and we received positive feedback from our partners.

Martin concludes:

“It’s very satisfying to see things coming in to place at the airfield, and although my time here is coming to an end, the work I have put in will help the Met Office team as we continue to support the Airport and the Island for some time to come.”

Martin Hopwood & Darren Hardy

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