WFO Charleston SC

STORM COURIER

National Weather Service Office Charleston September, 1999 Volume 3, Issue 2

5777 S. Aviation Ave. Charleston, SC 29406

843-744-0303

Dr. Gray's Atlantic Basin Hurricane forecast for 1999

The most active part of the hurricane season is here! Dr. William Gray, a noted hurricane researcher from Colorado State University predicts another active season (June 1-November 30) with a total of 14 tropical cyclones. Nine are expected to become hurricanes, and of these, four are forecast to become major hurricanes (i.e. Cat 3, 4 or 5 with winds greater than 110 mph). Seasonal averages for the Atlantic Ocean are 9.3 tropical storms, 5.8 hurricanes, and 2.2 major hurricanes.

Dr. Gray makes his preliminary forecasts for each season in November, with updates in April, June, and August to reflect observed West African rainfall, Pacific Ocean sea surface temperatures, upper level winds, and surface pressure patterns over the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea. This year, Dr. Gray and his researchers are providing probabilities of hurricane landfalls along the U.S. coastline. They give a 54% chance that one or more major hurricanes will make landfall along the U.S. East Coast, including peninsular Florida. This compares with a 100 year average of 31%.

The four year period from 1995-98 has been the most active span for tropical cyclones in recorded history with 53 named storms, including 15 major hurricanes . According to researchers at Colorado State University, we have already entered a period of increased tropical cyclone activity, similar to the period from the 1930's through the 1960's. Dr. Gray indicates that the increase in the Atlantic thermohaline circulation, resulting in warmer sea surface temperature anomalies across the Atlantic hurricane basin, may be responsible. He expects the next two decades will see increased hurricane activity similar to the past four years.

In This Issue:

1. 1999 Hurricane Forecast / Hurricane Preparedness Tips.

2. New Computer Power at The National Weather Service/Spotter News

3. Heat and Ultra-Violet (UV) Index

4. A Comparison of Junes in Charleston/Rains Return in a Big Way

5. The Heat is On Across the Lowcountry and Coastal Empire

6. Hurricane Dennis Brushes the Lowcountry and Coastal Empire

Visit our web page site

on the internet:

http://wchs.csc.noaa.gov



Includes local weather observations/forecasts & local historical/ climatological data for southeastern SC & GA.

Now is the time to make your hurricane plan.

* Know the hurricane risks in your area.

* Become familiar with your local hurricane evacuation route(s).

* Know where local emergency shelters are (even if you plan on staying).

* Devise a family plan of evacuation to a safe area...if ordered to by authorities (plan on staying at a motel/shelter).

* Obtain necessary materials to secure your home.

* Keep rain gutters and down spouts clear of debris.

* Determine a safe inland place to store your boat.

* Review insurance policy & find a safe place for important legal documents.

* Have a good supply of cash on hand since ATMs will not be accessible, if there is no power.

* Fill gallon jugs with enough water per person (5 gallons) for several days. The local water supply will likely be polluted.

* Do not forget a hurricane plan for your pet. Include places of shelter and a supply kit.

* Review the needs and working condition of emergency equipment such as flashlights, batteries, and portable radios.

* Do not wait until the Hurricane /

tropical storm watch is posted to do important chores such as filling up your automobile's gas tank. There may not be service at area stations until you get well inland.

* After a watch is posted for your area, insurance companies will not sell policies due to the increased risk...Insure your property/valuables now before the next hurricane.

* Always listen to authorities regarding evacuations. They know the dangers of staying in harm's way.

Page 1.


SPOTTER NEWS

Here are some of the Spotter reports for the spring severe weather season (March-June 1999). Thanks to the spotters, media, Law Enforcement, Emergency Management, and others who relayed these valuable reports. Also, thanks to everyone who attended the spotter training sessions held this past year. Your services are greatly appreciated.

BOC004-Casey Brown JAS112-Roy Ridgeway

BOC013-Charles Roberts JAS115-Peoples Svc. Station

BOC017-Edward Saxon JAS121-BP Tarboro

BUF130-Timothy McPheters JAS126-BP Ridgeland

CHS124-Chris Acklin JAS128-Piggly Wiggly

CHS134-Nancy Phillips JEN005-Earl Burke

CHS245-Tommy Garvin SCR002-Linda Vincent

CAN015-Shelia Sutton SCR011-Ted Burns

COL123-Robert Spires SCR012-Loretta Cosby

DOR134-Ronald Lee Bain SCR017-Larry Leeks

EFF020-Choo-Choo-Buildit Mart SCR020-Alvin Mock

EFF028-Graham's Grocery SCR024-Douglas Schiner sources

HAM115-Issac White SCR030-J.C. Warren

HAM116-SC Dpt. Of Natural Resources HAM118-Charles Campbell

HAM129-Youman's Farms Inc.

HAM130-Brighton Oaks Grocery

Severe weather reports to the National Weather Service

1. Call Us!!!

2.What did you observe? Tornado/Funnel cloud? Damaging Wind? Hail?Significant rains/snows? Other pertinent info?

3. When did you observe it?

4. Where did you observe it (Direction and distance from a known location)?

5. Where is it headed?

6. Other useful info...What is happening? Damage/Destruction?

New Computer Power at The National Weather Service

As a part of the modernization of The National Weather Service, the Advanced Weather Interactive Processing System (AWIPS) was installed in the Forecast Office in Charleston, South Carolina the last week of March 1999. AWIPS is a technologically advanced interactive computer system used to process, display, and transmit weather information. It is the cornerstone of the modernization and restructuring of the National Weather Service (NWS) and will allow the NWS to meet its mission "to provide weather and flood warnings, public forecasts, and advisories for all of the United States, its territories, adjacent coastal and offshore waters, primarily for the protection of life and property." Forecasters view large amounts of image, graphic, and alphanumeric information from many different sources on a daily basis. The AWIPS system will allow the forecasters the means to dissect this data in a more organized and user friendly environment.

The system can combine NEXRAD Doppler radar (WSR-88D) data with satellite imagery from the NOAA Geostationary Operational Environmental Satellites (GOES) and hundreds of observations from the Automated Surface Observing Systems (ASOS) often overlaying this data in one display to give the forecaster a three dimensional view of the atmosphere. Many different fields of model data are also available from the weather forecast models which are run on the mainframe computers by the National Centers for Environmental Prediction (NCEP) in Suitland Maryland. This is the same computer technology used by several branches of NCEP, including the Tropical Prediction Center (TPC) responsible for the forecasting of Tropical Cyclones including Hurricanes, and the Storm Prediction Center (SPC), which monitors and aids in locating those areas that are favorable for spawning severe thunderstorms and tornadoes.

Once the system has been given the final approval by its creators and testers, it will be used during severe weather events to issue Severe Thunderstorm and Tornado Warnings. The amount of information, and speed of viewing the information from a single scan of the radar will be dramatically increased. This system is expected to improve the decision making process so that forecasters can issue warnings with greater confidence and skill with a 6 GB hard drive. The individual workstations have either a 3 or 4 GB hard drive. The system remains a work in progress and future "builds" of the software will further improve AWIPS at the Charleston National Weather Service office. The entire system was designed by the Forecast Systems Laboratory in Boulder, Colorado which is a sister agency to the National Weather Service both of which are a part of the National Oceanic and Atmospheric Administration. AWIPS recently won top honors on June 7 in the Computerworld Smithsonian Awards program in the category of Environment, Energy and Agriculture. This award honors organizations that use technology in an innovative way to benefit society.

 

Page 2.

 

The Heat Index

Heat index (HI), also referred to as the apparent temperature, is a measure of the contribution humidity makes when high temperatures reduce the body's cooling ability. The HI is the temperature the body senses based on normal humidity levels. For example, if the actual temperature is 100 degrees with 40% relative humidity, the effect of this on the body would be the same as 111 degrees with normal humidity for that temperature. Refer to the HI chart at right. The National Weather Service (NWS) generally issues heat advisories when the index reaches 105 degrees for at least two consecutive days.

In an effort to alert local authorities and the general public, the NWS will highlight excessive heat /humidity conditions in its forecasts and statements through the release of appropriate safety rules and civil emergency messages.

Ultra-Violet Index

The National Weather Service issues this daily index for selected cities. It describes the next day's peak exposure to UV rays (scale 1 - 10+ ). This value is broadcast on NOAA weather radio daily.

Index: Exposure

0-2 Minimal

3-4 Low

5-6 Moderate

7-9 High

10+ very high

 

Page 3.

 

A Comparison of Junes in Charleston

Many folks around the greater Charleston area have commented about how much "cooler" it felt this June as compared to June last year. Looking at the statistics from Charleston International Airport bears this out. The average high temperature in June 1998 was a sweltering 93.2. This past June, however, was a full 8 degrees cooler for the highs (85.2). Overnight lows were also warm last June, with the average 72.4, while June 1999 recorded an average of 67.6. What was astonishing about June 1998 was the relentless heat combined with high humidities that sent heat indices soaring past 110 for several days. A total of 24 days had high temperatures of 90 or better in 1998. One of those days hit the century mark (30th). There was a stretch from June 12th to the 30th where highs were 90 or better. There were only six days in June 1999 that temperatures reached 90 or better, with the highest reading for the month at 91 on three days. Also, record highs were either tied or broken on three days in June 1998-99 on the 28th and 29th (tied records set in 1978 and 1936, respectively), with the 100 on the 30th setting a record for the date (previous 99 set in 1936). No records were set in June 1999. Both Junes were dry, with precipitation totals falling well below the normal of 6.43".

Here are the statistics for the last two Junes in Charleston:

June 1999 June 1998

Avg. High 85.2 Avg. High 93.2

Avg. Low 67.6 Avg. Low 72.4

Monthly Avg. 76.4 Monthly Avg. 82.8

Depart. from norm -1.9 Depart. from norm +4.5

Monthly High 91 (3 days) Monthly High 100 (30)

Monthly Low 60 (1) Monthly Low 53 (8)

Precip. 2.32" Precip. 3.41"

Depart. from norm -4.11" Depart. from norm -3.02"

Rains Return in a Big Way!

Many sections of the Lowcountry and the Coastal Empire of Georgia have had near drought conditions for the last several months (from February to June) as high pressure has dominated the area, not allowing for springtime storm systems to bring normal rainfall as well as the usual development of summertime thunderstorms.

On June 29th, the rains returned in a very big way over some areas. An area of showers and thunderstorms developed along and just off the coast from southern Charleston county to Bryan county Georgia. Multiple convergence zones focused on extreme southern South Carolina into southeastern Georgia during the mid morning through afternoon. Extremely heavy rainfall occurred in a short period of time across that region. Severe flooding was reported in the Beaufort and Savannah areas as well as other sections of Beaufort, Jasper and Chatham counties. A state of emergency was declared in Chatham county, including Savannah, through the 30th. The malls in Savannah were hit hard, and were closed as cars floated by in the parking lots. A cooperative observer in Hardeeville (southern Jasper county of South Carolina) reported a total of 15 inches of rain in about 12 hours. By 2 PM on the 29th, 11.4 inches had fallen at DeRenne Station in Savannah, while other parts of the city only received two to three inches. Beaufort reported a total of 11" in two days (28-29), which included 7.5" in 12 hours on the 29th. Savannah Airport received about 10" from June 26th to July 1st, including 6.6" which occurred on the 29th. According to Doppler radar estimates, some areas around southern Jasper and Beaufort counties received from 20-25" of rain between June 26th and July 1st. For more information about the flooding event, the Savannah Morning News has a special section on their Internet web site called Savannah Now Underwater.

Page 4.


The Heat is On Across the Lowcountry and Coastal Empire

Oppressive heat and humidity gripped south coastal South Carolina and southeastern Georgia during late July and early August due to a stubborn upper level high pressure system that stalled across the southern United States from mid July through August 1st. High temperatures in the mid 90s to mid 100s combined with dewpoints in the mid 70s to lower 80s to produce dangerous heat index values, especially from July 30th to August 1st. Heat index readings were in the 115 to 120 degree range. Record high temperatures were either tied or set, including an all time record at Charleston International Airport on August 1st. Beaufort and the downtown Charleston location at the Customs House also tied their all time record high temperatures.

The charts below show the records set and previous records. Records that were tied appear in bold italics.



Charleston (CHS)

Record

High

Previous Record High Minimum Previous Record Previous All-Time Previous Monthly
7/30/99 100 98 - 1942
7/31/99 101 100 - 1942
8/1/99 105

99 - 1990 81 80 - 1933 104 - 7/19 & 20/1986 102 - 8/14/1995


Charleston Downtown Record High Previous Record High Minimum Previous Record Previous All-Time Previous Monthly
7/26/99 100 98 - 1977
7/27/99 100 98 - 1949 80 80 - 1948
7/28/99 83 82 - 1993
7/29/99 99 96 - 1952 85 82 - 1949
7/30/99 82 81 - 1949
7/31/99 97 97 - 1961 84 81 - 1958
8/1/99 103 98 - 1970 86 81 - 1958 103 - 7/22/1977 102 - 8/5/1954


Savannah (SAV) Record High Previous Record All-Time Monthly Record High
7/31/99 101 101 - 1990 & previous years
8/1/99 102 101 - 1986 105 - 7/20/1986 104 - 8/5/1954

 

Beaufort

(NBC)

Record High Previous Record High Minimum Previous Record Previous All-Time Previous Monthly
7/30/99 100 100 - 1941
7/31/99 101 100 - 1941 88 79 - 1933
8/1/99 104 99 - 1941 83 80 - 1986 104 - 7/15 & 22/1932 102 - 8/5 & 6/1954 & 8/27/1938

Page 5.



National Weather Service
5777 S. Aviation Ave

Charleston, SC 29406

HURRICANE DENNIS BRUSHES LOWCOUNTRY AND COASTAL EMPIRE

After a slow start to the 1999 hurricane season, late August erupted with a flurry of tropical activity. Three tropical cyclones developed at the same time in the Atlantic, including Dennis. Tropical depression five developed north of the Greater Antilles on August 23rd, and moved slowly west northwest toward the Bahama Island chain while slowly strengthening. On the afternoon of August 24th, the fourth named storm, Dennis, developed. The tropical storm slowly developed reaching hurricane strength two days later on August 26th. Dennis raked the northwest Bahamas with hurricane force winds, and continued on a westerly track threatening the Florida east coast and both hurricane watches and tropical storm warnings were issued on the 27th.

The National Hurricane Center in Miami anticipated a change in the forecast track to northwest, and eventually north, as Dennis came under the influence of a large upper level trough across the East Coast, and had mentioned that the Carolinas would be most threatened during the upcoming days. On the evening of the 28th, a hurricane watch was issued from Savannah, Ga. to Surf City, NC. Tropical storm warnings would be issued for the entire South Carolina coast later that night. On the evening of the 29th, the category two hurricane with maximum sustained winds of 105 mph came within 110 miles of Charleston, SC. Since the Southeast Georgia and Southern South Carolina coasts were on the weaker western side of the hurricane, wind and rainfall effects were greatly reduced. Tropical storm force wind gusts, 39 to 73 mph, were felt along coastal sections of South Carolina, and rainfall was generally less than 2 inches across the tri-county area. Dennis paralleled the Carolina coast, and became stationary just off the Outer Banks of North Carolina while weakening. And now the rest of the story! Tropical Storm Dennis, after much meandering around, finally decided to make its move into North Carolina, making landfall just east of Cape Lookout late in the afternoon of September 4th.

As many Lowcountry residents are well aware, it's quite a different story experiencing the fringe affects of a category 2 hurricane, than experiencing a direct hit by a major hurricane, category 3-5, like Hurricane Hugo in 1989. At the time of this writing, the most active part of the hurricane season is yet to come. Names of storms like Hazel, Gracie, and Hugo will forever remain etched in our minds . Let's not let our guard down, remain prepared, as we recall those memorable storms made landfall in late September through mid October.

Page 6.

 


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