High Impact Weather Update #3: Significant Flooding and Wind Damage Possible From Helene. 5:00pm Update

High Impact Weather Briefing

Tropical Storm Helene
Forecast for North Carolina Foothills
Updated: 5:00pm Tuesday 9/24/24
Valid: Tonight – 9pm Friday

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Key Messages for Tropical Storm Helene:

• Helene’s Path and Impacts: Helene is expected to intensify and approach near-hurricane strength as it moves toward the Gulf of Mexico. Significant impacts, including heavy rainfall, storm surge, and potential hurricane-force winds, are expected along the Gulf Coast, and these conditions will progress inland as the storm moves northward.
• Flood Risks: Areas across the Southeastern U.S., including the North Carolina Foothills, are at risk for flash flooding from heavy rainfall associated with the storm. A Flood Watch has been issued, meaning conditions are favorable for flooding; residents should be prepared to act. A Flood Warning may follow if flooding becomes imminent.

Potential Hazards:

• Flooding Risk: High
• Tornado Risk: Medium
• Tropical Storm Winds: Medium

Forecast Rainfall (Tuesday – Friday Night):

• Expect scattered heavy rains from thunderstorms due to a stalled frontal boundary Tuesday, Tuesday Night, and Wednesday. Flash flooding will be possible Tuesday Night through Wednesday Night. That then sets the stage for significant flash flooding from Thursday evening through Friday night.
• Rainfall Totals:
  • Locally up to 12+ inches in some areas.
  • 7-10 inches in the central Foothills.
  • 5-7 inches in the lower regions.

Flash Flood Potential:

• Tuesday: Low risk of localized flash flooding due to slow-moving thunderstorms.
• Wednesday: A cold front stalling over the area will increase flood potential, particularly in counties like Polk, Rutherford, McDowell, Burke, and Caldwell. 4 – 6 inches of rain is possible in those counties even before Helene arrives Thursday.
• Thursday: High risk of flash flooding as heavy rainfall develops area-wide, with the greatest risk in the eastern slopes and adjacent foothills.
• Friday: Torrential rainfall will be ongoing, with extreme flash flood risk likely along the southern slopes.
• Saturday: As Helene lifts north, scattered heavy rains may trigger additional localized flash flooding due to an upper level low pressure center over the Ozarks.

Wind Forecast (Thursday Evening – Friday Night):

• Peak Wind Gusts (Be prepared for these peak gusts to potentially increase depending on how strong Helene gets over the Gulf of Mexico.
  • Hickory: 27 mph
  • Marion: 28 mph
  • Morganton: 25 mph
  • Lenoir: 26 mph
  • Shelby: 29 mph
  • Rutherfordton: 29 mph
  • Taylorsville: 25 mph
• Tropical Storm Force Wind Probability: There is a medium probability of experiencing tropical storm-force winds across the region, which could lead to widespread power outages. Residents are encouraged to prepare accordingly.

Risk Assessment (Thursday – Saturday):

• Confidence Level: Medium confidence that a significant weather event will occur, including flash flooding, strong winds, and possible severe weather. Preparation is key as conditions evolve.

Flood Watch vs. Warning:

• Flood Watch: Flooding is possible; stay tuned to trusted news sources.
• Flood Warning: Flooding is imminent; take immediate action to move to higher ground.

Hazard Timelines:

• Wednesday: Flooding risk begins medium, escalating to high by the evening. Tornado and wind risks remain zero.
• Wednesday Night: High flooding risk overnight with extreme risk developing by early morning. Wind and tornado risks are increasing.
• Thursday: Flooding risk continues to rise, with high risk during the evening. Tornado and wind risks increase through the day.
• Thursday Night: Extreme flooding risk overnight with significant wind and tornado threats.
• Friday: Flooding remains extreme in the morning, gradually decreasing. Tornado and wind risks remain present.