Hurricane Season Flood Alerts

Today’s Hurricane Season Flood Alerts

The Hurricane Season Flood Alert System (HSFAS) is based on forecasted precipitation amounts and seeks to provide communities with flood warning services as a key climate change adaptation and public safety tool. Alerts are provided to communities that have Flood Risk Mapping Studies (FRMS) or have published intensity-duration-frequency (IDF) curves from which precipitation based flood triggers can be derived. The HSFAS is to help communities in the province prepare for storms and avoid future high-cost expenditures in repairs and damages. The HSFAS is operational during the peak hurricane months of June to December. A list of the communities for which alerts are currently provided is shown below.

The report in the Adobe PDF file below has a table that is divided into two categories. These are:

  • An alert for “Areas with Flood Risk Mapping and Precipitation Induced Flooding” indicates a potential of flooding based on our flood risk mapping studies. The flood alerts are based on FRMS. All of the studies and mapping for the 1:20 and 1:100 AEP flood events are available on our Department’s webpage: www.mae.gov.nl.ca/waterres/flooding/frm.html. The studies defined the 1:20 and 1:100 Annual Exceedance Probability (AEP) flood event and associated precipitation events.
  • An alert for “Areas with EC IDFs but no Flood Risk Mapping” is based on the IDF curves from Environment Canada for that specific area. Consequently, it does not reflect any historical flooding but indicates a historically rare event.

Today’s Hurricane Season Flood Alert (260 KB)

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Current Streamflow Conditions

Existing conditions on rivers and lakes can impact whether a precipitation event leads to flooding.  If water levels are already high the chance of a precipitation event leading to flooding will be increased.   The map in the link below represents current streamflow conditions.  The colored dots on this map depict streamflow conditions as a percentile, which is computed from the period of record for the current day of the year. Only stations with at least 20 years of record are used.  A percentile is a value on a scale of one hundred that indicates the percent of a distribution that is equal to or below it. For example, on the map of daily streamflow conditions a river discharge at the 90th percentile is equal to or greater than 90 percent of the discharge values recorded on this day of the year during all years that measurements have been made.  In general:

  • a percentile greater than 75 is considered above normal
  • a percentile between 25 and 75 is considered normal
  • a percentile less than 25 is considered below normal

Current Streamflow Conditions

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Hurricane Season Forecast and Post-Season Reports

The NOAA’s 2021 Atlantic Hurricane Seasonal Outlook predicts an above-normal season (60%), followed by a 30% chance of near-normal season and a 10% chance of a below-normal season. Colorado State University (CSU) predicts above-normal activity. It is worth noting that the NOAA uses a 30-year (1981-2010) based-climatology and the CSU has updated their 30-year climatology to include (1991-2020). Meanwhile, Tropical Storm Risk (TSR) predicts that the 2021 Atlantic hurricane season is expected to be 25-30% above the long-term (1950-2020) normal and 5-10% above the recent (2010-2020) ten-year normal.

Wood anticipates an above-normal Atlantic Hurricane season and a normal to slightly above-normal storm track across Atlantic Canada, specifically affecting Newfoundland and Labrador with extratropical storms. There is a moderate risk of a tropical storm and a low risk of a hurricane making landfall in Newfoundland.

Detailed Documents

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Hurricanes, Flood Damages and Climate Change

Flooding is a natural event, but often has devastating effects on our lives and properties. These can be minimized by proper planning, state-of-the-art flood forecasting and flood alert systems and appropriate flood control strategies.

In Newfoundland and Labrador, floods in the fall of the year are the most costly in terms of flood damages.

Below is a graph with a seasonal breakdown of Disaster Financial Assistance Arrangements (DFAA) Damage Estimates. As illustrated, Fall events result in the greatest dollar value flood damages.

Bar chart displaying seasonal flood damage estimates from 2000-2010. View table below for data.
Total DFAA Flood Damage Estimates by Season from 2000-2010
Season Flood Damage Estimates ($)
Winter $15,530,308
Summer $15,589,602
Spring $32,388,278
Fall $101,014,638

Flooding in the fall is typically caused by weather systems that originate as hurricanes. The damage path from hurricane based weather systems is typically widespread as was observed for Hurricane Igor in 2010.

Floods, public safety and climate change are integrally linked. Due to climate change, the frequency and intensity of extreme precipitation events such as hurricanes that result in flooding is expected to increase. Climate change altered precipitation patterns will result in new communities experiencing regular floods and communities with existing flooding issues experiencing more intense and extensive flooding incidents.

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The Hurricane Season Flood Alert System

The Hurricane Season Flood Alert System (HSFAS) is based on forecasted precipitation amounts and seeks to provide communities with flood warning services as a key climate change adaptation and public safety tool.

Alerts are provided to communities that have Flood Risk Mapping Studies (FRMS) or have published intensity-duration-frequency (IDF) curves from which precipitation based flood triggers can be derived. The HSFAS is to help communities in the province prepare for storms and avoid future high-cost expenditures in repairs and damages.

The HSFAS is operational during the peak hurricane months of June to December.

The communities for which alerts are currently provided are listed in the Table below and depicted in the following map.

Communities / Areas with Precipitation Triggers for Hurricane Season Flood Alerts

Precipitation-based flood triggers 1:20 (mm) 1:100 (mm)
# Community (Area) Watercourse 12h 24h 12h 24h
FRMS
1 Appleton/Glenwood Gander River 60 78 75 99
2 Bishops Falls Exploits River 60 78 75 99
3 Carbonear Island Pond Brook, Powell’s Brook 74 95 95 117
4 Great Codroy (Codroy Valley) Grand Codroy River, South Branch 98 – 121 –
5 Cold Brook, Kippens (Gaudon’s Brook) Cold Brook, Gaudon’s Brook 69 – 86 –
6 Corner Brook Corner Brook Stream, Bell’s Brook, Petrie’s Brook 54 66 62 76
7 Deer Lake, Steady Brook (DEER LAKE A) Deer Lake, Humber River 54 63 66 76
8 Glovertown Terra Nova River 60 78 75 99
9 Petty Harbour, St. John’s (Goulds) Cochrane Pond Brook, Doyle’s River, Raymond Brook, Third Pond, Petty Harbour River, Dirty Bridge River, Goulds Stream, Second Pond, Third Pond, Fourth Pond, Fourth Pond Brook 96 110 121 137
10 Mount Pearl, St. John’s Waterford River 77 91 95 111
11 Hant’s Harbour Halfway Brook, Short’s Brook 74 95 95 117
12 Happy Valley-Goose Bay (GOOSE A) Otter Creek and Seven Other Creeks 50 62 62 75
13 Heart’s Delight-Islington (Heart’s Delight) Heart’s Delight Brook, Brook No. 1, Brook No. 2 74 95 95 117
14 Hickman’s Harbour-Robinson Bight (Hickman’s Harbour) Tween Bridge Pond to harbour – 85 – 115
15 Hodges Cove tidal basin behind causeway – 85 – 115
16 Logy Bay-Middle Cove-Outer Cove Outer Cove, Coakers River, Drukens River, Kennedy’s Brook, Outer Cover Brook 96 110 121 137
17 Portugal Cove-St. Philip’s Main River, Murray’s Pond River, Broad Cove River – 112 – 136
18 Salmon Cove Salmon Cove River 74 95 95 117
19 Clarenville (Shoal Harbour) Shoal Harour River – 82 – 115
20 Stephenville Noel’s Pond, Warm Creek, Blanche Brook 79 105 102 136
21 Stephenville Crossing, Black Duck Siding St. George’s River, Harry’s River 79 105 102 136
22 Bay Roberts (Shearstown) Shearstown Brook 76 90 108 132
23 Trout River Trout River 75 93 93 116
24 Victoria Salmon Cover River 74 95 95 117
25 Whitbourne Hodge River 74 95 95 117
26 Winterton Western Pond Brook 74 95 95 117
IDF
1 Argentia (ARGENTIA (AUT)) NA (IDF location) 141 153 198 210
2 Battle Harbour (BATTLE HARBOUR LOR) NA (IDF location) 51 69 62 86
3 Burgeo (BURGEO NL) NA (IDF location) 85 102 101 123
4 Churchill Falls NA (IDF location) 44 52 55 64
5 Comfort Cove (COMFORT COVE) NA (IDF location) 62 72 84 91
6 Daniel’s Harbour (DANIELS HARBOUR) NA (IDF location) 75 105 97 139
7 Gander (GANDER AIRPORT CS) NA (IDF location) 61 77 76 98
8 La Scie (LA SCIE) NA (IDF location) 66 78 84 96
9 Mary’s Harbour (MARY’S HARBOUR A ) NA (IDF location) 51 71 64 92
10 Nain (NAIN A) NA (IDF location) 52 63 64 78
11 Channel-Port aux Basques (Port Aux Basques) NA (IDF location) 92 115 133 145
12 St. Alban’s (ST ALBANS) NA (IDF location) 95 142 116 183
13 St. Anthony (ST ANTHONY) NA (IDF location) 58 78 70 97
14 St. Lawrence (ST LAWRENCE) NA (IDF location) 93 108 114 134
15 Wabush (WABUSH LAKE A) NA (IDF location) 43 54 53 67
Image of Community Locations for Hurricane Season Flood Alerts
Community Locations for Hurricane Season Flood Alerts

The HSFAS Alerts are based on site specific weather forecasts that are generated by Wood as a result of examining many of the available models from Environment Canada, the US National Oceanic and Atmospheric Administration, and WOOD’s in-house implementation of the Weather and Research Forecast model. Examining maximum precipitation predictions from many different dynamic models allows Wood to produce a better forecast of the maximum precipitation potential based on the strength of different models in handling the atmospheric physics of differing weather patterns. Furthermore, Wood also examines the various model precipitation outputs within a given radius of each community/area. This allows Wood to identify potential flood situations where a particular model may have accurately modeled precipitation amount or identified a flood situation but erred in the placement of its location.

These site specific precipitation forecasts are then directly linked to each site’s past flooding history through precipitation triggers. The precipitation triggers are derived from flood risk mapping studies and IDF curves. These precipitation triggers are summarized in Table 1.

The Water Resources Management Division correlates the HSFAS Alerts from Wood with water flow rates in the province’s river systems. This information is sent to Emergency Services Division who then alert the affected communities and coordinate responses

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