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Sincerely,
Ed Hopkins
The following highlights of the national weather have been extracted from the surface weather map for late Sunday night.
WILL DENNIS BE A MENACE? -- The major weather feature on the national weather map was Hurricane Dennis, which was moving northward along the South Carolina Coast toward North Carolina late Sunday night. Dennis, the first hurricane of the season to directly affect the East Coast, is an intense low pressure system that developed over the tropical Atlantic Ocean near the eastern Bahamas late last week and was carried toward the west-northwest on the broad flow of easterly winds (winds from the east) that are typically found across the tropics and portions of the subtropics.
The late Sunday night surface analysis charts do not show the strong winds and the tightly packed concentric isobars surrounding the system, because Dennis, like most hurricanes, is a relatively small diameter system, meaning that most of the isobars that indicate an intense low pressure system remained offshore. As of midnight Eastern Time, the center eye -- a distinctive feature of the hurricane -- had a diameter of approximately 35 miles. The northern portion of the eye wall containing the strongest near surface winds and the most intense thunderstorms surrounding the eye was located about 85 miles southeast of Mrytle Beach, SC or about 100 miles south of Wilmington, NC. Sustained surface winds in the eye wall were estimated to be near 105 mph, and the central pressure was 963 mb or 28.44 inches of mercury. As result, Dennis was a category 2 hurricane on the five-category Saffir-Simpson Hurricane Intensity Scale.
The region of hurricane force winds, exceeding 75 mph, extended outward from the system, but still remained offshore. However, a band of tropical storm force winds, with winds between 39 and 74 mph, were found to extend across portions of eastern South Carolina and coastal North Carolina, where more than 2 inches of rain had fallen. A buoy off Cape Fear, NC reported ocean waves to heights of 30 feet. The winds spiraling around the center of the hurricane in a counterclockwise direction were onshore and from the northeast across North Carolina, but from the northwest across portions of South Carolina. Movement of Dennis was to the north-northeast at about 14 mph.
Dennis is expected to continue to move toward the north to north-northeast through the nighttime hours of early Monday morning, slowly approaching the Carolina Coast. Some forecasts suggest that the hurricane may continue to turn more toward the northeast and remain off the coast. Regardless of the future track, the winds, the high seas and the heavy rains are expected to remain a problem for coastal residents. Hurricane warnings for winds in excess of 75 mph were in effect for the North Carolina coast, extending from Little River Inlet, SC to Cape Hatteras, and including Pamlico Sound. Tropical storm warnings for winds between 39 and 74 mph were in effect from Oregon Inlet on the North Carolina Outer Banks to Chincoteague, VA, to include the North Carolina Sounds and the southern portion of Chesapeake Bay. Mandatory evacuations were begun across various coastal counties of North Carolina, to include essentially all the barrier islands. The northeasterly winds (from the northeast) around the northern side of Dennis could cause coastal flooding, high surf and extensive beach erosion, especially on the barrier islands.
A COOL CANADIAN AIR PUSHES SOUTH -- A large high pressure system associated with a cool air mass was moving slowly to the east-southeast. As of Sunday night, the center of this large high pressure cell was located north of Lake Superior. Winds spiraling in a clockwise direction out of the high were bringing cooler air southward across the northern tier of states. The leading edge of the cool air was a cold front that stretched from Canadian Maritimes southwestward across the Middle Atlantic States and then westward into the Ohio and mid-Mississippi Valleys before turning northwestward and merging with a stationary front over the Plains.
The high pressure system is expected to continue to move slowly toward the east-southeast, reaching a position to the northeast of Lake Huron by Monday morning. The cold air is expected to continue to expand southward across the eastern half of the country, as the cold front pushes southward toward the Tennessee Valley by morning.
Because of the cold air mass, coupled by the weak winds and clear skies associated with the high pressure system, temperatures were expected to fall into the mid 30s across portions of the western Great Lakes. Frost advisories in effect for portions of north central and northeastern Wisconsin and Michigan's Upper Peninsula?
THUNDERSTORMS ACROSS THE PLAINS -- As of late Sunday evening, a region of strong to severe thunderstorms was located over southwestern Kansas near Dodge City. Doppler radar indicated winds in excess of 55 mph and hail of approximately 1 inch diameter. Earlier on Sunday evening, severe thunderstorms were also reported across portions of South Dakota and Nebraska and eastern Colorado, where a funnel cloud was spotted near Akron. Weak funnel clouds were also reported near Sioux Falls, SD.
The storms across the northern Plains were associated with a weak low pressure disturbance that was developing along a stationary front that stretched across the Plains from southeastern Alberta to western Missouri. As its name implies, little movement of this stationary front is expected into Monday. A slight risk of strong to severe thunderstorms over the western Plains will continue into Monday morning.
THE HEAT CONTINUES ACROSS THE GULF COAST -- Relatively clear skies and hot weather continued across the South, extending from western South Carolina to Texas on Sunday. The presence of Hurricane Dennis just to the east contributed to the clear skies and warm conditions in Georgia and interior portions of the Carolinas. The circulation associated with the hurricane often produces large scale sinking of air some distance to the west and northwest of the system, resulting in the dissipation of clouds and increased temperature readings. Record high temperatures for the date were either tied or set across Florida at Melbourne (96 degrees), Miami Beach (95 degrees), Palm Beach (95 degrees) and Hollywood (93 degrees). Over the weekend, other record highs were tied or set across the Gulf Coast states.
WET WEATHER ACROSS THE SOUTHWEST -- Even though high pressure was situated over southern Colorado and the Four Corners area, widely scattered afternoon and evening thunderstorms continued to develop in the mountainous regions, as a result of the influx of moisture across the Southwest. Heavy rainfall from these thunderstorms caused some local flash flooding across the lower Colorado Valley, to include portions of western Arizona, southern Nevada and southeastern California. Additional isolated thunderstorms produced rainfall of more than 2 inches and the potential for flash floods across southern Utah and western Colorado, where mudslides were reported. Unfortunately, wildfires continue across California and other states consuming more than 200,000 acres.
A REMINDER -- Lightning remains one of the major causes for weather-related deaths nationally. A wife of a Kansas State football coach died Saturday from injuries sustained by lightning while jogging during a thunderstorm more than two weeks ago.
TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- On Sunday, the lowest temperature reported in the continental U.S. was 34 degrees at Mammoth Lakes, CA, while Sunday's highest temperature was 107 degrees at Parker and Lake Havasu City, AZ.
ALASKAN WEATHER -- A storm system consisting of a low pressure system centered over the Bering Sea and a accompanying occluded front (a hybrid between a cold and warm front) that stretched southeastward across the Alaska Peninsula brought clouds, rain and windy weather to the Aleutians and the Alaska Peninsula. Cold Bay and Dutch Harbor had winds to 40 mph. Farther east, mostly clear skies were found across the Kenai Peninsula. A low pressure system centered in the eastern Gulf of Alaska brought cloudy skies to northern portions of the Panhandle.
An east-west oriented stationary front was positioned across northern Alaska near the Arctic Circle, separating cold air over the North Slope from slightly milder air across interior Alaska. Clouds were found across much of the northern portion of the state. As of Sunday afternoon, light snow continued to fall at Barrow, while Deadhorse had snow earlier.
On Friday morning, Barrow reported the first snow of the season as a cold front passed, accompanied by snow flurries. The last snow was on 29 June, a day before the end of the official 1998-1999 snow season.
The lowest overnight temperature in Alaska as of Sunday was 21 degrees at Eagle, and the midafternoon highest statewide temperature was 70 degrees at Tanana.
HAWAIIAN WEATHER -- A large high pressure system situated over the North Pacific to the north of Hawaii should continue to influence the weather across the islands through Tuesday. The clockwise circulation around this high pressure cell produces easterly or northeasterly winds on the southern flank of the cell. These winds from the east or northeast are known as trade winds, are typically found across the islands, as well as much of the tropical regions of the Northern Hemisphere. As a result of the strong high pressure system, the trades are expected to remain brisk, within a 15 to 30 mph range. Some light showers are expected to move across Kauai and the other islands. Small craft advisories were in effect for state waters. A buoy along the equator south of Hawaii reported ocean swells on Sunday that could reach the south shores of the islands by late Monday and produce high surf on Tuesday.
From the files of the Aviation Weather Center, Kansas City, MO and Intellicast
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Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 1999, The American Meteorological Society.