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 10 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 2024 Atlantic Hurricane Seasonal Outlook predicts an 85% chance of an above-normal season, followed by a 10% chance of a near-normal season and a 5% chance of a below-normal season. Both Colorado State and Tropical Storm Risk forecast Accumulated Cyclone Energy (ACE) which is aggregate measure of storm intensity, duration, and number. ACE biases toward long-lasting intense hurricanes rather than weak tropical storms because long-lasting intense hurricanes are more likely to cause destruction. Colorado State is predicting a seasonal ACE of 210, which is well above the 1991-2020 average of 123. Meanwhile, Tropical Storm Risk (TSR) is predicting a seasonal ACE of 217, also well above the 30-year climate normal..

The forecaster anticipates an above normal season for the province, with the greatest risk of tropical storms, hurricanes, and strong post-tropical storms across eastern Newfoundland, including St. John’s. These types of storms carry the associated risk of high wind gusts of more than 100 km/h, heavy rain of more than 100 mm with associated flooding, and storm surge flooding on exposed coastline near sea level..

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) 12h 24h 12h 24h
FRMS        
1 Appleton/Glenwood 65 85 81 108
2 Bay Roberts 76 90 108 132
3 Bishops Falls 69 88 92 120
4 Brigus 98 110 124 137
5 Burnt Islands 85 113 104 142
6 Carbonear 98 110 124 137
7 Channel-Port aux Basques 85 113 104 142
8 Clarenville 97 109 128 143
9 Corner Brook 54 66 62 76
10 Cox’s Cove 54 72 66 89
11 Deer Lake 56 70 69 87
12 Ferryland 98 110 124 137
13 Glovertown 74 88 95 113
14 Grand Falls-Windsor 69 92 88 120
15 Great Codroy (Codroy Valley) 85 113 104 142
16 Hant’s Harbour 98 110 124 137
17 Happy Valley-Goose Bay 50 62 62 75
18 Heart’s Delight-Islington 98 110 124 137
19 Hickman’s Harbour 96 109 127 142
20 Hodges Cove 102 115 135 151
21 Isle aux Morts 85 113 104 142
22 Kippens 78 101 100 127
23 Logy Bay-Middle Cove-Outer Cove 96 110 121 137
24 Mount Pearl, St. John’s 106 102 135 149
25 Parsons Pond 72 98 91 125
26 Petty Harbour, St. John’s (Goulds) 96 110 121 137
27 Placentia 127 114 173 194
28 Portugal Cove-St. Philip’s 96 110 121 137
29 Rose Blanche 85 113 104 142
30 Rushoon 97 119 125 154
31 Salmon Cove 98 110 124 137
32 Steady Brook 56 70 69 87
33 Stephenville 78 101 100 127
34 Stephenville Crossing 79 102 105 136
35 Trout River 72 98 91 125
36 Victoria 98 110 124 137
37 Whitbourne 104 117 138 153
38 Winterton 98 110 124 137
IDF
        
1 Argentia (Argentia Auto) 134 152 183 204
2 Badger 81 98 104 126
3 Blanc Sablon, L’Anse au Clair 59 73 73 90
4 Bonavista 117 113 160 181
5 Burgeo 89 104 106 124
6 Churchill Falls 44 54 54 66
7 Comfort Cove 63 74 79 93
8 Daniel’s Harbour 69 98 87 126
9 Englee 104 130 137 172
10 Gander 65 85 81 108
11 Hopedale 44 60 56 76
12 La Scie 65 80 81 97
13 Mary’s Harbour 56 70 71 88
14 Nain 51 63 63 77
15 Shefferville 49 67 62 86
16 St. Alban’s 93 137 111 173
17 St. Anthony 60 77 74 96
18 St. Lawrence 101 130 127 167
19 Terra Nova National Park 83 96 105 122
20 Twillingate 57 71 69 87
21 Wabush 43 54 53 67

The HSFAS Alerts are based on site specific weather forecasts that are generated by the forecaster as a result of examining many of the available models from Environment Canada, the US National Oceanic and Atmospheric Administration, and the forecaster’s in-house implementation of the Weather and Research Forecast model. Examining maximum precipitation predictions from many different dynamic models allows the forecaster 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, the forecaster also examines the various model precipitation outputs within a given radius of each community/area. This allows the forecaster 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 the forecaster 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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