With hurricane season’s arrival, hits on the Bermuda Weather Service website are starting to take off as weather watchers check for storms.
With that in mind, the BWS has made some subtle changes to try to present storm information more clearly.
It is hoped this will give people a better understanding about each storm’s potential impact on Bermuda and encourage them to stay alert as forecasts are amended.
Michelle Pitcher, the BWS director, said that the service issued a tropical update bulletin on the website whenever there was a tropical storm or hurricane forecast to be near, or directly affecting, Bermuda.
“These images have a map in the middle showing where the forecasted track is and the extent of the winds associated with the storm in reference to Bermuda,” Ms Pitcher said.
“Then we have information on the top and bottom of that map with more information about the actual tropical storm or hurricane.
“Part of the information underneath the map is a statement that states the ‘Closest point of
approach to Bermuda within 72 hours (3 days) is forecast to be ‘X’ nautical miles to the ‘direction’ at ‘date and time’. However, this system may move closer to Bermuda after this time period, depending upon its track.”
Getting the key message right
Feedback received on the graphic in recent years showed that people were confused by the final sentence, as well as the phrase “closest point of approach within 72 hours”.
After sending examples of different wording and requesting suggestions from stakeholders, Ms Pitcher said the BWS had rejigged it in a way that was “hopefully less confusing”.
She said: “Now it’s going to state, ‘Within the next 72 hours (3 days) the nearest forecasted point to Bermuda is expected to be ‘X’ nautical miles to the ‘direction’ at ‘date and time’. Please note that the forecast is subject to change and this point may move closer to or further away from Bermuda. See future advisory updates’.”
Ms Pitcher added: “The reason we use 72 hours is because that’s a key time period for emergency management. And while the arrival of the centre of a storm is important, we don’t want people solely focused on it as conditions can start to deteriorate well in advance of the storm’s arrival.”
Less uncertainty equals greater knowledge
Every year, the National Hurricane Centre improves its forecasting track of a tropical cyclone, which means the cone of uncertainty – where the centre of the storm may go – becomes narrower.
“On a hurricane tracking map, you can see there’s a shaded area on either side of the centre line. That’s the cone of uncertainty,” Ms Pitcher said.
“The centre line is where the forecast of the storm’s centre is, and the shaded area on either side of that line represents the uncertainty, meaning the centre of a storm could go anywhere within that shaded area.
“This year, the shaded area has shrunk by 5 per cent. It doesn’t sound like much, but considering what they are forecasting, every little bit is very important.”
Wind warnings – explained
Ms Pitcher said that the BWS maps also show different coloured circles for wind speed, and that it was important for people to understand what they meant
A red circle shows the extent of hurricane-force winds from the centre of the storm, yellow shows the extent of the 50-knot winds from the centre and blue shows the extent of tropical storm-force winds from the centre.
Ms Pitcher said: “Communicating the winds is not always straightforward, as there are times when we have tropical storm warnings noting something to the effect of ‘the western edge of the tropical storm-force winds are crossing over Bermuda’.
“We then can receive feedback from people saying, ‘well it’s not tropical storm-force winds where I am’, or ‘the airport sensors are showing sustained at 30 knots, not 34 knots’.
“The reason for that is that the winds are not constant around any tropical storm and some places will be sheltered from the full force of the winds.
“Winds can be patchy, especially toward the outer edges of the storm. So, while we might be under a tropical storm-force warning, if we’re just being caught by the edge of a tropical storm, we might not experience those strongest winds because they’re not consistent.
“The same can be said for the 50-knot winds and the hurricane-force winds. Our responsibility is not only for the island but the marine area which extends 25 nautical miles out from our shores.
“We do add extra information when able especially in situations when the strongest winds are forecast to impact only part of the marine area or maybe just reach one end of the island.
“We work directly with the specialists National Hurricane Centre to be able to give out the best possible information available so that the best decisions can be made to protect lives, livelihoods and properties.”
For your storm updates, visit www.weather.bm
