Storms

Isaias

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July 30, 2020

Update Fri Jul 31 0200PM EDT

Hurricane Isaias was producing maximum sustained winds of 75 mph and was centered in the Southern Bahamas, approximately 245 miles SE of Nassau. Movement was to the NW at 16 mph.

Since the morning update at 0800AM EDT, the forecast track has shifted slightly to the west. This increases wind risk for some locations along the east coast of Florida.

Here are the afternoon (200PM EDT) updates to the Hazard Area Likeliness (HAL) Map…these areas have changed since the previous post.

WIND – Likeliness of Tropical Storm Force Winds (39mph+) that can bring down trees and cause widespread power outages:

Cocoa Beach and Fort Lauderdale, FL have been upgraded to PROBABLE. This now means that tropical storm force winds are PROBABLE along Florida’s east coast from near Cocoa Beach and the Space Coast to Fort Lauderdale. Andros, Bahamas has been upgraded to LIKELY

STORM SURGE – Likeliness of storm surge exceeding 4 feet:

No changes since last update…

RAIN – Likeliness of 6 or more inches of rain:

No changes since last update…

Consult the uploaded map for the HAL index at each location… the text above only communicates the changes with this update.

Look for the next update on Friday evening.

HEAVY SURF AND COASTAL EROSION

Even with the eye of Hurricane Isaias likely tracking off the east coast of Florida, expect heavy surf and coastal erosion along the entire Atlantic Coast of Florida.

TIMING OF TROPICAL STORM FORCE WINDS

I posted a map showing the Earliest Reasonable Arrival Time of Tropical Storm Force Winds from the National Hurricane Center. The approximate arrival times based on map interpretation is as follows:

Fort Lauderdale: 0800AM Saturday
Palm Beach: 1000AM Saturday
Cocoa Beach/ Space Coast: 700PM Saturday
All times are approximate and subject to change.

I will update again this evening. Stay safe everyone.


Update Fri Jul 31 0830AM EDT

Hurricane Isaias is tracking through the Bahamas today and will approach the SE Florida coast on Saturday. Here are the morning updates to the Hazard Area Likeliness (HAL) Map…these areas have changed since the post at 1100PM last night…

WIND – Likeliness of Tropical Storm Force Winds (39mph+) that can bring down trees and cause widespread power outages:

Fort Pierce and Palm Beach, FL have been upgraded to PROBABLE…

New Providence, Bahamas has been upgraded to LIKELY…

STORM SURGE – Likeliness of storm surge exceeding 4 feet:

No changes since last update…

RAIN – Likeliness of 6 or more inches of rain:

Miami has downgraded to UNLIKELY

Consult the uploaded map for the HAL index at each location… the text above only communicates the changes with this update.

Look for the next update on Friday evening.


Update Thu Jul 30 1100PM EDT

Tropical Storm Isaias will impact Bahamas overnight and Friday and likely strengthen into a hurricane Friday night in Western Bahamas….will impact Southeast U.S. this weekend and early next week.

Hazard Area Likeliness (HAL) Map

This product forecasts the likeliness of wind and flood hazards at 24 locations in the southeast U.S. and Bahamas. Changes since last update:

WIND – Likeliness of moderate damage from tropical storm force winds exceeding 39 mph:

Tropical storm force winds at Tampa, Fort Myers and Naples, FL, are now UNLIKELY

STORM SURGE – Likeliness of a storm surge exceeding 4 feet:Storm surge exceeding 4 feet now UNLIKELY for Jax Beach, FL, and Brunswick and Tybee Island, GA.

Storm surge exceeding 4 feet now POSSIBLE for Cape Hatteras, Morehead City and Wrightsville Beach, NC

RAIN – Likeliness of 6 inches or more of rain:Rainfall exceeding 6 inches now POSSIBLE for Morehead City and Wrightsville, NC.

The text only lists changes. Please consult HAL map for hazard area likeliness- hazard risk not listed in the text if likeliness has not changed since the previous advisory.

Check back for updates at least twice daily as long as Tropical Storm Isaias threatens to impact the U.S. with wind and flood damage.


Thu Jul 30 1100AM EDT

Tropical Storm Isaias formed in the Caribbean over night. It technically formed late on Wed Jul 29, making it the earliest “I” storm on record. It broke the previous record, set by Tropical Storm Irene on Aug 7, 2005, by an impressive 10 days.

On Thu Jul 30 at 1100AM EDT, the center of Tropical Storm Isaias was located just south of the eastern tip of the Dominican Republic. Most of the convective activity (thunderstorms, heavy rain bands, etc.) was offset to the north and east of the circulation center, impacting portions of the Dominican Republic and Puerto Rico.

Structural disorganization of this system, coupled with the land interaction of mountainous Hispañola, has introduced complexities to the forecast and made both track and intensity forecasts less certain than normal.

It appears that the large circulation pattern of this system will enable it to survive the passage over Hispañola and emerge on the north side of the island as a weak to moderate tropical storm. Conditions are favorable for some additional strengthening Thursday night and Friday, once Isaias emerges into tropical waters north and west of Hispanola.

Increasing wind shear will temper the intensification on Friday and Saturday as it tracks to the northwest, and it will likely pass through the western Bahamas and approach Southeast Florida as a strong tropical storm, or possibly a category-1 hurricane.

Tracking and intensity forecasts should improve Thursday night after the center of circulation passes Hispanola. The mountains on this island are so large that they can severely obstruct the air flow of a tropical system, and sometimes cause the circulation center to re-develop in a slightly different location once it crosses the island.

All of these uncertainties affect the long-term track and intensity forecast, but many of our questions with this system should be resolved Thursday night.

With this update I have created the first Hazard Area Likeliness (HAL) map for Tropical Storm Isaias for the likeliness of moderate damage from tropical storm force winds (39 mph+), 4 feet of storm surge and 6 inches of rain.

Hazard Area Likeliness (HAL) Map for Tropical Storm Isaias
Thu Jul 30 1200PM EDT

WIND – Likeliness of Tropical Storm Force Wind (39mph+) POSSIBLE for all southeast U.S. coastal locations from Cape Hatteras, NC to Miami, FL. Also POSSIBLE for Naples, Fort Myers and Tampa on Florida’s Gulf Coast, and Orlando.

PROBABLE for three locations in the Bahamas: Grand Bahama, New Providence and Andros.

STORM SURGE – Likeliness of 4 feet of Storm Surge POSSIBLE for locations in extreme northeast Florida and Georgia. This includes Tybee Island, Brunswick and Jax Beach. Also POSSIBLE for the three locations mapped in the Bahamas.

The coastline from extreme SW South Carolina south to extreme NE Florida, including the entire Georgia coast is very vulnerable to salt water flooding from storm surge because of the shallow offshore water depth and concave shape of the coastline. Even if Isaias tracks offshore, a 4-foot storm surge is POSSIBLE in these areas.

RAIN – Likeliness of 6 inches of rain POSSIBLE from Cocoa Beach to Miami, Florida and PROBABLE for the three locations in the Bahamas. These probabilities are based on QPF rainfall forecasting and are subject to change considerably over the upcoming days.

I will update the HAL map at least twice daily as long as wind and flood impacts threaten the U.S.

Continue to monitor the progress of this storm and do not let your guard down. In recent years, Matthew (2016), Irma (2018) and Dorian (2019) spared direct strikes on Southeast Florida, but that does not mean that Isaias will do the same thing.

Take care everyone and stay safe!

—Hurricane Hal