Hurricane Hortense:
A fortuitous warning

By Alan Ruffman
Edited by Peter Zimmer. Design by Tony Seed

Hortense Hammered Halifax
Deaths in Lunenburg Co. and on Eastern Shore
$30 million in losses. Yacht clubs in chaos.

HALIFAX (CP) -- Hurricane Hortense slammed ashore early last evening just west of Lunenburg and left Nova Scotia reeling in its aftermath. The RCMP report at least ...
P. 1 article, Sunday, September 15, 1996,
The Daily Star-Chronicle, Halifax

Of course it did not happen that way. A year ago there were no deaths, and property damage was barely $3 million, as Hurricane Hortense struck Nova Scotia a glancing blow as it went by, dying at the cold northerly end of its ten-day trek from the Caribbean to its end a day later over the Grand Banks south of Newfoundland.

Hortense was the first tropical cyclone whose winds were still at hurricane strength (that is, with sustained winds of more than 118 km/hr) to touch Nova Scotia since Blanche hit in 1975. Hurricane Beth brushed by Nova Scotia in 1971, and Hurricane Edna sideswiped us in 1954. And the event seems essentially forgotten with the short-term memory loss we might generally attribute to the modern media amnesia. Hortense was last year's disaster. It might be another twenty-two years before another real hurricane tests our preparedness. Or it could be this month. Hurricanes are very unpredictable, even in areas where they are much more common.

And the event seems essentially forgotten with the short-term memory loss we might generally attribute to the modern media amnesia. Hortense was last year's disaster. It might be another twenty-two years before another real hurricane tests our preparedness. Or it could be this month. Hurricanes are very unpredictable, even in areas where they are much more common.

Our Nova Scotian police forces and Emergency Measures Organization (EMO) officials did not appear to anticipate the hurricane-specific dangers Hortense posed certain coastal regions: certainly no plans for evacuations from storm-surge vulnerable areas (Lawrencetown, Green Bay) were instituted in advance of the storm's arrival, as they should have been.

Repeated inquiries the author sent to all the municipal emos along our Atlantic Coast brought little response: not one indicted that they had hurricane evacuation schemes in place. Or that they've made such plans since Hortense. No municipality in Nova Scotia stated they have prepared maps to show areas susceptible to hurricane storm surge. Had a decision been reached to move families back from susceptible coastline areas, it seems the responsible Nova Scotian authorities would have had to improvise. Maps probably do not exist that define the first priority hazard areas for such an evacuation.

It is now clear, with the benefit of hindsight, that we were very lucky in Nova Scotia vis-a-vis Hurricane Hortense. Had this storm come ashore in the southwest part of the Province as a full-fledged Category 1 hurricane (perhaps with winds at 140 km/hr), rather than just barely brushing the northeast corner in its final dying stages, the damage costs could have easily been an order of magnitude higher (i.e. $30 million). And we likely would have lost lives.

Perhaps as often as once a century Category 3 hurricanes have come ashore in Atlantic Canada, with winds between 177 and 209 km/hr, winds which pack two to three times the force of Hortense's winds (and do on average almost four hundred times the property damage we experienced last September). As far as historical information is available no Category 4 or 5 hurricanes have been this far north. Already in 1997 the Maritimes have experienced the spent remnants of tropical storm Anna in early July, and most of us were hoping for some rain from the remnants of a decaying Hurricane Danny late in July (to no avail).

During 1995 Nova Scotia only saw the direct effects of two hurricanes: the thundering storm swells from Hurricane Felix twice pounded our Atlantic shores in August and in September the same from Hurricane Luis, passing well offshore.

In 1996 there was the approach and offshore passage of Hurricane Bertha and the heavy rains of Edouard as it headed for us, but then veered offshore. Our media gave considerable coverage of Hurricane Fran's transit across the southern United States coast and on into southwest Ontario. And in September we all saw the news reports of the impact of Hurricane Hortense as it tracked across northeastern Nova Scotia and then turned eastward to pass off the south coast of Newfoundland as a dying extratropical storm.

It's not just the winds

As it approaches Atlantic Canada from the open ocean, several aspects determine the power of a hurricane to affect our lives and property on shore: there are the hurricane-defining winds tearing at everything standing in their way; the wind drives the ocean onto (and sometimes over) our shorelines, in the form of towering storm waves and the less obvious storm surges that add to our normal tides; there are torrential rains, driven horizontally by the winds. And there is the storm's track, the path of the eye of the hurricane, and whether it passes you to it's left or right, and how far away it passes, and how quickly it travels.

And then your particular location on the land, where you stand to meet the storm (just back from beach-front, on a cliff-top, in a river valley inland, ...) will help determine what the storm's wind, rain and waves do to you and your property.

The Wind first
Winds of a tropical cyclone spiral counter-clockwise in the northern hemisphere in towards the eye of the storm (as seen from above, as in satellite images), getting stronger as they close in on the centre (or "eye"). When they are circling the eye with sustained speeds above 118 km/hr (74 mph) the storm is ranked as a hurricane.. A Category 5 hurricane (seldom seen in the Caribbean, probably never seen in these parts) has sustained windspeeds in excess of 247 km/hr (155 mph).

It's not just the hurricane winds whirling around the eye that affects the wind force you'll feel on the ground (or in a ship at sea): the storm as a whole is moving along the storm track, adding (or subtracting) its overall speed over the surface to the speed of the wind around the eye. If one stands on the track of a fast-moving hurricane and looks in the direction of travel, the winds on the surface are much stronger on the right-hand side of the track than on the left side. The last place one wishes to be during a hurricane is on the right side, or windy side, of a hurricane's track.

For Hortense (a dying hurricane with winds just above the minimum 118 km/hr and a forward velocity of about 34 km/hr) coming ashore on the Eastern Shore, the sustained wind speeds on the surface just to the right of the eye would have been about 118 plus 34 km/hr, or 152 km/hr (95 mph) while the winds to the left of the eye would be only 84 km/hr (118 minus 34). The wind to the right is 80 per cent faster than to on the left side.

But the force of the wind varies as the square of the velocity of the wind. For Hortense the destructive force of the wind was about three times greater on the right side (seaward side) than it was on the landward left side as she passed Canso.

The Ocean meets the shore: storm waves

The hurricane wind drives the ocean into big waves. In 1995 in the open ocean well off from Nova Scotia, Hurricane Luis created huge sustained 30 metre (100 foot) waves that severely hampered the Cunard luxury liner Queen Elizabeth II for several hours and provided spectacular wave data on Canada's offshore anchored wave-rider buoys. More normal storm wave heights would average in the 10 to 20 m range. Towards land, the bottom's profile can modify and limit and direct the waves' amplitudes and forces.

As with wind, the force of these waves, the energy they carry, increases as the square of their size and speed. Double the wave, and you've got four times the force. As the winds come ashore, so do the waves, transferring their colossal energies to the cliffs, boulders, beaches and dunes, and whatever we've built in these areas.

These waves pound cliffs into boulders, throw boulders onto cliffs, break the granite boulders into rocks, wharves into matchsticks, ships into scrap-metal, reshape beaches....

Off the harbour of Halifax the waves of Hortense peaked at 8.7 metres -- only three storeys tall.

And tides...

The storm waves ride on top of the ocean's surface. Here in Atlantic Canada we're very aware of the tides as the ocean itself rises and falls twice daily. And if we've paid attention at all, we know that during each month some tides, called spring tides, have a bigger range (rise higher, ebb lower) than the smaller neap tides. At the Halifax tide gauge the height of the biggest normal tides are about a half-metre higher than the month's lowest high tides.

Hortense went past Halifax close to high tide on the 15th of September. The highest tides of September occurred on the 1st and 28th. The lowest high tides were on the 7th and 21st.

and a Storm Surge...

But the astronomical tides are not the only forces that raise the level of the ocean; hurricanes (and other windstorms) can also produce a local increase in the height of the ocean's surface, and this is the storm surge.

The storm surge has two components; the low atmospheric pressure in the storm that "sucks" the ocean upwards (at the centre of the storm the pressure is lowest and the rise greatest), and the push of hurricane winds that piles up water before them (as well as churning the surface into the storm waves).

In mid-ocean the absolute height of the ocean doesn't really matter during a hurricane: at a coastline the story is much different. Strong onshore winds can rapidly pile up the nearshore waters onto the coast adding to the sea level rise from the low pressure. In fact the low pressure component turns out to be only 10 to 20 per cent of a typical hurricane's storm surge in the right quadrant of the storm: there most of the extra sea level is result of the wind's push.

The duration of the storm surge depends on the rate at which the storm is moving, hence for how long the strong winds act to pile up the coastal waters.

For most of the Canada's Atlantic coastal areas and for most hurricanes the counter-clockwise winds push a surge ashore as the storm tracks in from the south or southwest. Strong offshore winds can actually remove water from the coast, giving a negative storm surge.

and waves and tides and surge combined...

If the storm surge arrives along with, or persists through a normal high astronomic tide, then the hurricane damage will be compounded. The high tide and the storm surge add together to move anchored boats, float wharves, and shift shore properties to record heights. Further, the very high sea level surface serves to carry the extra high hurricane-whipped storm waves well inland to areas normally immune from any wave action.

For Hortense the surge was a metre or a bit more on the Eastern Shore. Measured off Halifax harbour, Hortense's storm surge combined with the day's high tide came within inches of matching the highest instantaneous water level recorded in the last thirty-five years. It was the highest since 1980. Had it come at a Spring high tide it would have been nearly a third of a metre (or about one foot) higher.

There are old reports of a storm surge in Newfoundland in 1775 that would have been about twenty feet. Some reports had thirty feet. (In your mind's eye, stand where you can see the ocean and raise its level as far as you can see by the height of a two-storey house, and then put big waves on it, waves the height of a three-storey building or more.)

The Saxby Gale of 1869 added its storm surge to the year's highest spring tides of the Bay of Fundy to flood Moncton, other towns along the Fundy shore and all the Fundy dykelands.

During Hurricane Andrew (Category 4, Florida), waves on top of the record storm surge rolled right through the second story corporate headquarters of Burger King in the Miami area. It could have been much worse. Though ocean levels rose in excess of 5.2 metres (17 ft.) over the normal astronomic tide during the storm surge along a portion of the Florida coast south of Miami, Hurricane Andrew's storm surge fortunately came at about the time of the normal astronomic low tide. Six hours earlier or later the waves would have had another metre or so of ocean to ride on.

On a rugged rocky, or cliff-like, coast, the storm surge and hurricane waves are of little consequence. However, on shallow, shelving shorelines, edged by sand beaches, low estuaries, marshes, or erodible soft rocks such as the red sandstone of Prince Edward Island, the extra rise of sea level can be dramatic and dangerous. In Atlantic Canada a storm surge of sixty centimetres (just two feet) is considered significant and the Atmospheric Environment Service and Canadian Hydrographic Service try to give the public warning of such events.

The Rain

A tropical cyclone draws up immense quantities of moisture from the warm sea offshore, then drops it as torrential rain, generally in the ‘northwest quadrant', i.e. on the forward left side of the hurricane. US meteorologists have developed a rule-of-thumb to predict the amount of rainfall (in inches) you'd expect to get if you are in this quadrant: divide 100 by the forward speed of the storm in knots. Shunpiking's research staff converted this to metric units: 5,000 divided by the forward speed in km/hr gives the approximate rainfall in millimetres.

Hortense's northwest quadrant passed over much of Nova Scotia and gave us some heavy rains that resulted in some local flooding. Hortense's rain fit the rule-of-thumb: its speed was about 18.2 knots or 34 km/hr and areas of Nova Scotia to the left of Hortense's track received 5.5 inches (140 mm) of rain in a matter of hours -- rather more than would fall here in the course of an average month.

If a hurricane stalls in its forward progress, then some areas can receive truly horrendous amounts of rain. Last month (July 1997) Hurricane Danny took almost four days to get from the Alabama coast across Georgia to the Atlantic coast. During that time some areas received a metre (40 inches) or more of rain. There was extensive flooding and lives were lost.

The streams, rivers, swamps, the natural (and man-made) drainage systems often cannot handle the deluge of hurricane rains. Flooding can be almost instant and catastrophic. Steeper slopes can become water-saturated and develop mudslides and slumps in the highly lubricated soils.

In 1954 it was the rain of Hurricane Hazel that caused the deaths of 81 persons in the Toronto area. Here in 1971 it was the rain on the left side of Hurricane Beth that tore out all the undersized culverts and undermined houses in Dartmouth as the swollen Dartmouth lakes sought their natural exit to the sea in downtown.

Our historical experience with hurricanes

While hurricanes are rare in our area, and Category Two or Three events even rarer, we have experienced them. And we will again, sometime, somewhere in Atlantic Canada.

Hortense should be taken as a fortuitous reminder.

There's lots of historical experience with both extratropical storms (hurricane remnants) and, less often, with full-blown hurricanes in the Atlantic Provinces. Some have been very serious and have been accompanied by large hurricane storm surges (see Timeline, below).

  • The first British invasion of Quebec City was aborted when the Boston-based armada of 1711 was driven ashore on the northern shore of the Gulf of St. Lawrence by what was probably a hurricane; 2,000 lives were lost.
  • The September 1775 hurricane that struck eastern Newfoundland may yet prove to be Canada's most tragic disaster with a reported 4,000 lives lost and a poorly documented, localized, sudden storm surge reported to be twenty or even thirty feet (six to nine metres!).
  • The Saxby Gale of October 1869 was a tropical cyclone that tracked into New Brunswick near the mouth of the Bay of Fundy during the highest of the year's high astronomic spring tides. The storm surge overtopped all the Bay of Fundy dykes, flooded the downtown business district of Moncton, and flowed onto the streets of Great Village and Maitland in Nova Scotia.
  • The August 1873 hurricane flattened whole forests in Cape Breton Island, drove anchored vessels far inland from the shore, and sank or destroyed over 1,100 vessels, with deaths approaching 600 in the Gulf of St. Lawrence and among the fishing fleet of the Magdalen Islands.

In Newfoundland the ‘August Gales' of 1927 and 1935 spawned folksongs among outport fishers. In 1944 an unnamed serious hurricane spent itself up the spine of Nova Scotia. Carol of 1953, Edna of 1954 and Beth of 1971 are still remembered clearly in some places.

Those who don't learn from
history are doomed to repeat it

Information about such storms go back over the past two hundred fifty years or so. Yet Canada does not have a systematically compiled hurricane climatology nor do we detail the northern ends of the significant hurricanes which we have suffered. There is not even a comprehensive list of the most serious historical hurricanes experienced in Atlantic Canada and no attempt has been made to ‘categorize' our most powerful hurricanes. It is work that is only just beginning.

At one time in the eighteenth and nineteenth centuries, hurricanes used to impose most of their tragedies offshore on vessel crews as they suddenly engulfed unsuspecting and helpless sailing vessels. This is no longer the case with modern radio and satellite warning systems and much more substantial vessels not dependent on the wind for propulsion. It is not the high winds and flying objects (or even the rain) that cause most hurricane deaths, or even the property losses now in North America. It is at the coastline that a hurricane now exercises its fury on humans and their built environment.

In North America, and throughout the world, coastlines have been under persistent development pressure with residential and recreational uses dominating the growth along the eastern seaboard of the United States and Canada. Where the developed coastlines are low and flat they are susceptible to storm surge and wave damage during hurricanes. Eastern Canada is not as guilty of this building trend since we have had lower population pressures and because we are regularly disciplined by the significant waves and winds of severe winter storms. We also tend to have more rugged, higher coastlines, save for parts of the Gulf of St. Lawrence; most structures are thus high enough to be safe from a hurricane's waves.

However Hurricane Hortense reminded us that we are not at all immune from the effects of hurricanes along our coastlines. Prevention and planning are by far the easiest and cheapest response. The most susceptible coastline areas can be defined and mapped, development controls for future building should be put in place, just as we do within the floodplains of rivers, and when the next tropical cyclone threatens, local police and fire department officials should know where to evacuate families, or to close roads, to prevent the loss of life. Weather forecasters in the Atmospheric Environment Branch, storm surge modellers in the Department of Fisheries and Oceans, Emergency Measures officials both federally and provincially, police and emergency response organizations, insurance companies, highway engineers, erosion specialists, municipal planners and their Councils, and residents of the Maritimes would all do well to take note of Hortense's warning. —Alan Ruffman

lan Ruffman is a marine geologist and geophysicist and president, Geomarine Associates Ltd. in Halifax. He has become a student of historical hurricanes of Atlantic Canada through his research on the major September 1775 hurricane. He has recently received a modest research contract from the Atmospheric Environment Service to document the 1869 ‘Saxby Gale' and is seeking all accounts of this hurricane. Alan was recently awarded a fellowship at the American Antiquarian Society's Library in Worcester, Massachusetts to further research the 1775 hurricane.

Information graphics:
Windspeed, Force and Damage by Peter Zimmer
Hurricane Gusts by Peter Zimmer
Timeline: Major hurricanes making landfall in Atlantic Canada, 1700-1996 by Peter Zimmer;
Hortense Storm Track, courtesy Geological Survey of Canada (Atlantic), "Hurricane Hortense Strikes Atlantic Nova Scotia: An Examination of Beach Response and Recovery", R.B. Taylor et al.

"Hortense was last year's disaster. It might be another twenty-two years before another real hurricane tests our preparedness. Or it could be this month. Hurricanes are very unpredictable…"