Tropical System Sally

Post Reply New Topic

KEY MESSAGES:

1. An extremely dangerous and life-threatening storm surge is now
expected, and a Storm Surge Warning is in effect for areas outside
the southeastern Louisiana Hurricane and Storm Damage Risk Reduction
System from Port Fourchon, Louisiana to the Mississippi/Alabama
border. Residents in these areas should follow any advice given by
local officials.

2. Hurricane conditions are expected by late Monday from Grand
Isle, Louisiana to Ocean Springs, Mississippi, including
Metropolitan New Orleans, with tropical storm conditions likely by
Monday. Preparations should be rushed to completion in those areas.

3. Sally is expected to produce flash flooding across southwest and
central Florida and prolong existing minor river flooding across
west-central Florida through Monday. Widesprea significant flash
flooding and minor to isolated major river flooding is likely across
portions of the central Gulf Coast Monday through the middle of the
week, with flooding impacts spreading farther into the Southeast in
the middle to late parts of the week.

KEY MESSAGES:

1. It is too early to determine where Sally's center will move
onshore given the uncertainty in the timing and location of Sally's
northward turn near the central Gulf Coast. Users should not focus
on the details of the official forecast track, since NHC's average
forecast error at 48 hours is around 80 miles, and dangerous storm
surge, rainfall, and wind hazards will extend well away from the
center.

2. An extremely dangerous and life-threatening storm surge is
expected for areas outside the southeastern Louisiana Hurricane and
Storm Damage Risk Reduction System from Port Fourchon, Louisiana, to
the Alabama/Florida border, where a Storm Surge Warning is in
effect. Residents in these areas should follow any advice given by
local officials.

3. Hurricane conditions are expected by late Monday within portions
of the Hurricane Warning area from Morgan City, Louisiana, to
the Mississippi/Alabama border, including Metropolitan New Orleans,
with tropical storm conditions likely to begin Monday. Preparations
should be rushed to completion in those areas.

4. Sally could continue to produce flash flooding across central and
northern Florida and prolong existing minor river flooding across
west-central Florida through Monday. Widespread significant flash
flooding and minor to isolated major river flooding is likely across
southeastern Louisiana, Mississippi, and Alabama through the middle
of the week. Flooding impacts are expected to spread farther across
the Southeast U.S. through the week.

SALLY BEGINS ITS ASSAULT ON THE NORTH-CENTRAL GULF COAST LATE TODAY

Based on everything we know, a slow-motion disaster will start today, peak tomorrow, and last into Wednesday along the southeast Louisiana, Mississippi, and possibly the Alabama coast. Damaging effects will be felt well inland as well.

Tropical Storm Sally is slowly organizing and strengthening. It is forecast to reach hurricane strength by the time the center reaches the coast tomorrow. Exactly how strong it will be is an open question. The storm still has a short window of time in fairly conducive atmospheric conditions. Residents need to be ready for a formidable hurricane.

Worse than the strength of the storm, however, will be the duration of the high winds on the coastline. High winds over an extended period can do more damage than somewhat stronger winds that come and go.

The current forecast is for a Category 1, but the National Hurricane Center acknowledges that there is significant uncertainty in that prediction. Residents and emergency planners need to be ready for a Category 2, at least.

Even with that, the worst of this storm is not likely to be the wind. Sally’s slow crawl as it nears the Louisiana or Mississippi coast will exacerbate the other impacts of the storm as well.

The Gulf water is forecast to be pushed as much as 7 to 11 feet over normal high tide levels, in part because the storm is moving slowly. The water is pushed onshore for a longer period in a slow-moving storm, so the surge builds up.

Water rise will occur as far east as the inland waterways around Destin and Panama City in the Florida Panhandle, although there it’s not expected to be life threatening if people don’t get caught in it. The forecast is for 1 to 3 feet of water above normal high tides.

The rainfall forecast keeps increasing. Now, with a stronger storm creeping ashore, up to 2 feet of rain is forecast, with widespread amounts of about a foot from the New Orleans Metropolitan Area to Pensacola and the western Panhandle. Heavy rains will move well inland through the rest of the week, and that water will have to drain to the coast, aggravating the flood threat.

The slow movement of the storm also adds uncertainty to the forecast. Storms move slowly because the steering currents are weak, but that means that small factors can change the path. As we saw in Hurricane Laura, a small shift in the landfall point makes a big difference in how much storm surge occurs at points near where the center comes ashore.

If the center moves over or west of New Orleans, Sally could cause higher winds in the heart of the city than Katrina, which tracked to the east and slammed the Mississippi coast. The Katrina disaster was due to the flood-wall failures prompted by the storm surge.

The post-Katrina New-Orleans-area levees and flood protection system should not be challenged by Sally, but the areas outside those giant levees are at significant risk. Depending on the exact track, some of the levees protecting smaller communities may be topped.

Full hurricane preparations in the entire impact zone need to be completed immediately. And all residents must carefully follow local instructions. There is a large-scale effort underway to keep people safe.



Hurricane Paulette is moving past Bermuda after passing directly over the island early this morning. The entire island was in the eye. The storm was estimated to have top sustained winds of 90 mph at the time of landfall, which was a little less than forecast. We’ll have to wait for word on how they did.

KEY MESSAGES:

1. It is too early to determine where Sally's center will move
onshore given the uncertainty in the timing and location of Sally's
northward turn near the central Gulf Coast. Users should not focus
on the details of the official forecast track, since NHC's average
forecast error at 36 to 48 hours is around 60 to 80 miles, and
dangerous storm surge, rainfall, and wind hazards will extend well
away from the center.

2. An extremely dangerous and life-threatening storm surge is
expected for areas outside the southeastern Louisiana Hurricane and
Storm Damage Risk Reduction System from Port Fourchon, Louisiana, to
the Okaloosa/Walton County Line in the Florida Panhandle, where a
Storm Surge Warning is in effect. Residents in these areas should
follow any advice given by local officials.

3. Hurricane conditions are expected late tonight or early Tuesday
within the Hurricane Warning area in southeastern Louisiana and are
expected by late Tuesday and Tuesday night within the Hurricane
Warning area along the Mississippi and Alabama coastlines and the
western Florida Panhandle. Tropical storm conditions are likely to
begin this evening in these areas and preparations should be rushed
to completion.

4. Life-threatening flash flooding is likely, as well as widespread
minor to isolated major flooding, on area rivers along and just
inland of the Central Gulf Coast. Significant flash and urban
flooding, as well as widespread minor to moderate river flooding is
likely across Mississippi and Alabama through the middle of the
week. Flooding impacts are expected to spread farther across the
Southeast through the week. Sally could continue to produce flash
flooding across the Florida peninsula and prolong existing minor
river flooding across west-central Florida through today.

KEY MESSAGES:

1. Historic and catastrophic flooding is unfolding along and just
inland of the coast from west of Tallahassee, Florida, to Mobile
Bay, Alabama. In addition, widespread moderate to major river
flooding is forecast. Significant flash and urban flooding, as well
as widespread minor to moderate river flooding, is likely across
inland portions Alabama into central Georgia. Widespread flash and
urban flooding is possible, as well as widespread minor to moderate
river flooding, across western South Carolina into western and
central North Carolina. Scattered flash and urban flooding is
possible, as well as scattered minor river flooding in southeast
Virginia.

2. Life-threatening storm surge is occurring along portions of the
coastline from Alabama to the western Florida Panhandle, including
Pensacola Bay and southern portions of Mobile Bay.

3. Hurricane conditions are expected this morning and then continue
into this afternoon within portions of the Hurricane Warning area
along the Mississippi and Alabama coastlines and the western Florida
Panhandle.

After two days spent spinning less than 150 miles off the coast of Alabama, Florida and Mississippi, Sally finally made its move to come ashore Wednesday morning, unleashing up to 30 inches of rain, 100 mph wind gusts and a six-foot storm surge.

Areas in coastal Alabama and the western Florida Panhandle were hardest hit. By Wednesday evening, the worst weather had departed these areas, but flooding rain had spread inland over eastern Alabama and southwest Georgia.

The National Hurricane Center warned that “historic and catastrophic flooding, including widespread moderate to major river flooding” was continuing to unfold.

As Sally made landfall as a Category 2 hurricane near Gulf Shores, Ala., at 5:45 a.m., fierce winds cut power to more than 500,000 customers in Alabama and Florida. Its surge inundated Pensacola in nearly six feet of water, the third-highest level on record.

At 5 p.m. Wednesday, Sally had weakened to a tropical storm with 60 mph winds, but the flooding threat continued as heavy rain expanded into Georgia and was expected to reach the Carolinas on Thursday.

While in the Gulf of Mexico, Sally picked up tremendous amounts of moisture from the warm waters, which it is wringing out as heavy rainfall over the Southeast.

The storm deviated from forecasts calling for it to stay at the same level of intensity and instead rapidly intensified shortly before landfall, going from an 80 mph Category 1 storm to a 105 mph Category 2 storm between 8 p.m. Tuesday and 2 a.m. Wednesday.

On Wednesday evening, heavy rain had exited the hard-hit zone stretching between Pensacola and Mobile, but severe flooding continued in some areas because of rising rivers. The most intense rain was focused inland in southeastern Alabama and southwest Georgia, with flood warnings expanding into this area.
Into Thursday, the Hurricane Center expected significant flooding in inland portions of eastern Alabama and central Georgia. Thursday into Friday, heavy rain and flooding was forecast to spread from western South Carolina through much of North Carolina and into southeast Virginia.
At 5 p.m., the storm’s peak winds were near 60 mph as it headed northeast at 7 mph. It was forecast to weaken to a tropical depression by Thursday morning.
A tornado watch was in effect until 7 p.m. Wednesday for southern Alabama, the Florida Panhandle and southwestern Georgia.