Showers, some heavy moved in on Sunday June 1st. A post-frontal trough rotated around a stalled low to the distant north of Bermuda and convergence along it allowed significant shower activity to move in. In some of the heavier showers, the temperature plunged due to evaporational cooling – reaching a new daily record of 63.1F at the airport. This comes as highs are running 5-6F below climatology because the stalled low to our north is continuing a northwesterly flow across the island, bringing in cooler, less humid air from eastern Canada.
Expect a few showers tonight and tomorrow morning as the low to our north drifts southwestwards, towards us. Temperatures increase through the week, back to more seasonal levels. See the latest official forecast from the Bermuda Weather Service here.
June 1st also marked the official start to Hurricane Season 2014. The Bermuda Weather Service just finished its annual Hurricane Awareness Week promotions and I would like to echo that now, while the season is young and quiet, is the time to stock up on long-lived supplies and to develop/revise a preparedness plan. This year’s hurricane awareness week gave particular focus to maritime impacts of tropical cyclones for Bermuda, and the role of Hurricane Hunters in forecasting these storms.
1. Maritime impacts of Tropical Cyclones
The gale, storm, and hurricane force winds found in Tropical Cyclones whip up the ocean into a frenzy. Large swells emanate hundreds of miles from the center of these systems. These swells result in coastal erosion, strong coastal currents, and can generally be hazardous for small craft. It is NOT safe to venture into the waters in these conditions, even if winds remain relatively light and precipitation holds off.
Further, if a tropical cyclone’s track takes it closer to shore, powerful onshore winds allow sea water to pile up along the coastline on top of normal astronomical tides. This phenomenon is what is known as “storm surge”. Storm surge can result in devastating coastal flooding and erosion, particularly at high tide. In addition to this coastal inundation, large battering waves can accompany the storm surge inland making it more dangerous. An estimated storm surge of between 8 and 11ft impacted Bermuda’s southern coastline resulting in extensive damage to the airport and extreme coastal erosion along south shore. More recently, Hurricane Igor generated a storm surge of unknown height that flooded parts of the town of St. Georges.
It is important to be aware of these ocean threats – many of us neglect them, thinking that wind and rain are the only components of these systems. Know if you are in an area prone to coastal flooding and have a plan in place in case of a coastal flooding related threat or emergency. Make sure boats are properly secured sufficiently in advance of inclement weather as to not endanger life.
Terms to know (From BWS Glossary):
Swell– Surface gravity waves on the ocean that are not growing or being sustained any longer by the wind. Generated by the wind some distance away and now propagating freely across the ocean away from their area of generation, these waves can propagate in directions that differ from the direction of the wind.
Storm Surge – An abnormal rise in sea level accompanying a hurricane or other intense storm, and whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge is usually estimated by subtracting the normal or astronomic high tide from the observed storm tide.
The Reef – For the purpose of the marine forecast, the reef can be interpreted as being the main northern reef, rather than the narrow fringing reefs on South Shore. Note that no forecast is specifically for sea state in enclosed waters, such as the Great Sound. These sea states would be covered by “Seas inside the reef….”.
Wave Height – The vertical distance between a wave crest and the preceding or following wave trough.
2. Hurricane Hunters
The US Air Force and National Oceanic and Atmospheric Administration each have a set of hurricane hunter aircraft tasked to fly into these violent cyclones to gather crucial data. Flying at low altitude, these aircraft drop weather instruments called ‘dropsondes’ into key storm structural elements to get critical information about the position and intensity of the Tropical Cyclone they are investigating. Further, surface measurements are taken constantly as they fly through the storms, guided by onboard weather radar and the expertise of the Meteorologists at the National Hurricane Center based in Miami, FL.
Data gathered from these flights provides forecasters with otherwise unavailable observations from within the core of Tropical Cyclones hundreds of miles from land. Some of these observations are fed into computer models to improve their output and these observations can be used directly by National Hurricane Center meteorologists to determine how well they are estimating storm position and intensity. The advance notice this gives forecasters helps them provide earlier notice for public preparations.
This invaluable information aides significantly in the protection of life and property in the event that a Tropical Cyclone impacts land. Hurricane Hunter information and the services of the National Hurricane Center are provided to all of the Atlantic and East Pacific at the cost of the US Government. Incredible advances in Tropical Cyclone track and intensity forecasting have come from Hurricane Hunter reconnaissance missions and the priceless information gleamed therefrom. This is what allowed the National Hurricane Center the confidence to issue warnings with more lead time – for example, hurricane warnings are now issued 36hours ahead of the onset of adverse weather, an increase from the 24hours notice prior to 2010.
Terms to know (From BWS Glossary):
Hurricane Warning – A Hurricane Warning shall be issued when: Sustained winds of 64 knots or more are expected to affect Bermuda within 36 hours, associated with a tropical cyclone or a subtropical cyclone.
Hurricane Watch – A Hurricane watch is issued when: Sustained winds of 64 knots or more may possibly affect Bermuda, within 48 hours, associated with a tropical cyclone or a subtropical cyclone.
Small Craft Warning – When winds of mean speed 20 to 33 knots and/or seas of 9 feet or greater are forecast to begin affecting the marine area within the next 36 hours a Small Craft Warning will be issued.
Tropical Storm Warning – A Tropical Storm Warning is issued when: Sustained winds of 34 to 63 knots are expected to affect Bermuda, within 36 hours, associated with a tropical cyclone or a subtropical cyclone.
Tropical Storm Watch – A Tropical Storm Watch is issued when: Sustained winds of 34 to 63 knots will possibly affect Bermuda, within 48 hours, associated with a tropical cyclone or a subtropical cyclone.
As always, the message is to be alert and prepared. One significant storm makes it a bad year.