Charlie Paxton "Weather Patterns" NDPA Symposium 2012

Weather Patterns and

Social Aspects Associated

With United States Rip

Current Deaths

Charlie Paxton Science and Operations Officer

National Weather Service Tampa Bay Area

INTRODUCTION

Shepard (1936) first used the term “rip

current”:

• A circulation pattern of accumulated water

from waves rapidly flowing back out to sea

through narrow channels in the surf zone.

What is a Rip Current?

A strong

narrow (~10m)

current flowing

seaward.

Sand Bars at Low Tide

Shore break area

Outer sand bar

Deep channel

2010

64 Rip Current

29 Lightning

45 Tornado

0 Hurricane

34 Cold

42 Winter

33 Wind

Deeper water - waves don’t break.

It’s deceiving!

Types of Rip Currents

Types of Rip Currents

Flash: Short duration current (less than 10 minutes)

Unpredictable temporary conditions and variable

locations.

Types of Rip Currents

Traveling: Long

shore current)

pushes rip away

from original

location.

May push swimmer

into Flash,

Permanent, or Fixed

Rip current.

Wave Generation

Stronger wind, longer fetch = stronger waves

Wave energy is proportional to

amplitude or height squared

Waves of various sizes and

periods (speeds) are generated

Wave Period

• The longer the

period between waves: • The longer the

waves. • The faster the

waves move. • The more

momentum the waves carry.

Rip Current Animation

More drownings near low tide

0

2

4

6

8

10

12

14

16

No. of

Drownings

Hi

to

1

1

to

2

2

to

3

3

to

4

4

to

5

5

to

Lo

Lo

to

1

1

to

2

2

to

3

3

to

4

4

to

5

5

to

Hi

Tidal Times

Swell Period vs. Rip Currents

Stronger winds create

longer period swells

that move faster, have

more energy -

invigorate rips

Wave

Period

seconds

Wave

Speed

ms-1

5 8

6 9

9 14

11 17

13 19

14 21

How much current does it take?

Choppy conditions with

longer period waves

Choppy and

confused

conditions

may mask

someone

struggling in a

rip current.

Rip Current Reports

METHODOLOGY

Rip current death and injury reports were collected

from National Weather Service (NWS) Storm Data

(NCDC 2010).

The first rip current death and injury records were

entered by some NWS offices in 1994.

Other NWS offices have only begun providing records

within the past several years.

The Great Lakes, Hawaii, and Alaska areas were not

examined.

Injuries are typically listed in Storm Data when a near

drowning victim is taken to a hospital.

Top five states with rip current deaths

(Storm Data 1994-2009)

Top 5 States Deaths Injuries Coastline

Florida 234 199

2173 km

1067 km

(beaches)

California 43 97 1352 km

North Carolina 36 14 484 km

Alabama 23 2 85 km

New Jersey 22 27 209 km

Top five Florida counties with rip

current deaths (Storm Data 1994-2009)

Top 5 Florida

Counties

Deaths Injuries

Broward 32 41

Escambia 31 46

Miami-Dade 20 13

Walton 20 1

St. Johns 19 1

Florida divided into four regions

Beach Attendance Factors

•Season

•Weather

•Air Temp

•Time of day

•Water Temp

•Day of week

Water Temperatures

Rip current deaths typically occur in water is > 20 C.

Cold water decreases stamina and leads to muscle

cramping and hypothermia and alcohol increases

effects.

Alabama resort areas had 4 April cases but none

between November and March.

Florida Panhandle - 8 rip days in March and 11 in

April.

In California, someone has been killed or injured by

rip currents during every month.

U.S. rip current deaths by day of

week (Storm Data 1994-2009)

Ages

The average ages of victims was around 30.

California - youngest average age (26).

Florida - oldest average age (39).

In Florida the average age for rip current

deaths along the Southeast Coast was 45.

• 13% were 70 or older and under 5% the other

Florida regions.

CASE STUDY – Black

Sunday June 8th 2003

Eight People died on Black

Sunday in rough surf along

the Florida Panhandle”.

This was a terrible beginning

to an ill-fated summer with

20 Florida Panhandle rip

current deaths

Escambia and Walton

Counties are in the top five

Florida counties for rip

current deaths

Date County Deaths

09 May Santa Rosa 1

09 May Escambia 1

11 May Escambia 1

31 May Gulf 1

08 Jun Walton 6

08 Jun Okaloosa 2

09 Jun Escambia 1

02 Jul Bay 2

13 Jul Bay 1

30 Aug Escambia 2

31 Aug Escambia 2

Total 20

Rowan et al. (2004) in a Florida Department of Health study found:

8 of 12 drowning victims were male

10 were from out of state

3 had detectable levels of alcohol.

8 who drowned were attempting to rescue

someone who was struggling in the

water.

Most of those struggling were later saved.

Rowan et al. (2004)

Median age of the drowning victims was

46.5 years.

3 of the 12 drownings occurred in the

morning, and nine occurred in the

afternoon.

One of those who drowned was Larry

Lamotte, a CNN correspondent.

a. Surface chart b. Wind flow and speed (ms-1

)

Friday June 6th 2003

Complex Weather Pattern

Rain and Building Surf

Saturday June 7th 2003

Rain and Building Surf

a. Surface chart b. Wind flow and speed (ms

-1)

Buoy 42036 wind direction and speed 200 km west northwest of Tampa, FL

Buoy 42036 wave height and wave period 200 km west northwest of Tampa, FL

Black Sunday June 8th 2003

The rain has ended the waves have not

a. Surface chart b. Wind flow and speed (ms-1

)

Wind and Sea Level Pressure Averaging

METHODOLOGY

Winter = November through April.

Summer = May through October.

Surface wind (ms-1) and Sea level pressure

(hPa) mean and anomaly patterns were

examined using NCEP reanalysis data (Kalnay

et al., 1996) through the interface at

http://www.esrl.noaa.gov/psd/.

Data plotted from day 0 to day -4 (4 days

before the event day)

METHODOLOGY

Areas Examined

Florida

• Panhandle

• Southwest

• Southeast

• East

Texas

Alabama

South Carolina

North Carolina

Delaware

New Jersey

New York

California

South-

east

Florida

Summer

Increasing

easterly

flow

Figure 1c.1 Southeast Florida Summer Vector Wind (ms-1) Wind anomaly (ms-1) Sea level pressure (hPa) Day 0

-1

-2

-3

-4

Day -4

Figure 1c.1 Southeast Florida Summer Vector Wind (ms-1) Wind anomaly (ms-1) Sea level pressure (hPa) Day 0

-1

-2

-3

-4

Figure 1c.1 Southeast Florida Summer Vector Wind (ms-1) Wind anomaly (ms-1) Sea level pressure (hPa) Day 0

-1

-2

-3

-4

Day -3

Figure 1c.1 Southeast Florida Summer Vector Wind (ms-1) Wind anomaly (ms-1) Sea level pressure (hPa) Day 0

-1

-2

-3

-4

Day -1

Figure 1c.1 Southeast Florida Summer Vector Wind (ms-1) Wind anomaly (ms-1) Sea level pressure (hPa) Day 0

-1

-2

-3

-4

Day -1

Figure 1c.1 Southeast Florida Summer Vector Wind (ms-1) Wind anomaly (ms-1) Sea level pressure (hPa) Day 0

-1

-2

-3

-4

Day 0

Alabama

Winter

Increasing

southerly

flow

Figure 3.2 Alabama Winter (4 cases) Vector Wind (ms-1) Wind anomaly (ms-1) Sea level pressure (hPa) Day 0

-1

-2

-3

-4

Figure 8.1 New York Summer Vector Wind (ms-1) Wind anomaly (ms-1) Sea level pressure (hPa) Day 0

-1

-2

-3

-4

New

York

Summer

Increasing

Southerly

flow

Tropical Storm Ophelia near Florida and

Hurricanes Maria and Nate swells affecting New York and New Jersey 7 September 2005

California

Summer

Figure 9.1 California Summer Vector Wind (ms-1) Wind anomaly (ms-1) Sea level pressure (hPa) Day 0

-1

-2

-3

-4

DAY 0

CONCLUSIONS

Typical weather patterns influencing rip currents are

associated with the subtropical high at the lower

latitudes and by more transient low pressure

systems in the higher latitudes

Onshore winds create greater rip current death

conditions.

Onshore winds create choppy disturbed waves that

are more likely to catch a swimmer by surprise

Rough conditions may also mask or hide someone in

distress from potential rescuers.

CONCLUSIONS

The results from this study are intended to provide

guidance for issuing rip current forecasts several

days in advance of the events.

Records vary from state to state.

Some factors are not easily discernable such as the

individual’s abilities and experience.

Most rip current deaths and injuries occur during the

warmer months and on weekends when more people

are at the beach

Future work: Related nearby buoy data to drownings.

Standardized

signage at many

beach access

points

Education

Where do most rip current

deaths occur?

At

unguarded

beaches!

Lifeguards

save lives