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The following discussion is based upon a review of the surface weather map for late Monday night. Several major weather features appeared:
The following discussion is based upon a review of the surface weather map for late Monday night.
DENNIS BRUSHES THE CAROLINA COAST -- After moving to the northwest toward the South Carolina coast on Sunday, Hurricane Dennis took a turn toward the north-northeast early Monday morning as it approached the Outer Banks of North Carolina. This tropical low pressure system, that at one time had sustained surface winds of at least 105 mph, continued toward the northeast during Monday and paralleled the coastline, but remaining out to sea. By late Monday night Dennis had moved to a position some 145 miles east of Cape Hatteras, NC. Winds near the center had dropped to 90 mph. Central sea-level pressure measured by hurricane reconnaissance aircraft near the center of the eye was 974 mb (28.76 inches of mercury). The surface weather analysis maps do not reflect the intensity of Dennis, because of its relative small size, coupled by its position off shore. Hurricane force winds (74 mph or greater) extended outward approximately 100 miles from the system's center.
While Hurricane Dennis did not make landfall, its effects were felt along the Carolina coast. Many locations had tropical storm force winds (39 to 74 mph), with higher gusts, causing some damage. The onshore winds helped pile water toward the shore causing heavy surf, coastal flooding in some locales and considerable coastal erosion. Estimates of from 6 to 8 inches of rain fell across coastal North Carolina. As of Monday afternoon, at least 3 deaths were attributed to Dennis.
Dennis is expected to slow its forward speed by Tuesday and continue to weaken as the central pressure increases slowly. However, the strong high pressure system across the Northeast should maintain a strong pressure gradient between the high and the advancing hurricane, resulting in continued strong winds around the northern semicircle surrounding Dennis. The position of this high pressure system could also mean that Dennis may stall and conceivably make a turn toward the west and toward the Middle Atlantic Coast.
Hurricane warnings for the North Carolina coast were dropped on Monday night, but tropical storm warnings were continued for the Atlantic Coast from Cape Lookout, NC to Chincoteague, VA, to include southern Chesapeake Bay. High surface advisories were in effect as far north as New York's Long Island, where swimming along the beaches was banned.
COOL WEATHER MOVES TOWARD THE NORTHEAST -- A large Canadian high pressure system continued to move slowly toward the east-southeast on Monday, spreading a cool air mass across a large portion of the Great Lakes, Midwest and the Northeast. As of late Monday night, the center of this high pressure cell was located near Ottawa, ON, having moved eastward from a position on Sunday night that was to the north of Lake Superior. The clockwise circulation of winds around this high pressure system produced northerly winds (from the north) across New England and along the East Coast, while southeasterly and southerly winds were found across portions of the mid- and Upper Mississippi Valleys, as well as the Dakotas.
The southern extremity of the cool air mass had been a cold front became stationary across the Southeast and lower Mississippi Valley. By Monday night, this front stretched southward along the Carolina coast from just to the north of Hurricane Dennis in the North Atlantic to southern Georgia, where the front turned westward and then west-northwestward, continuing across the Gulf Coast states before reaching Arkansas, where the front took a more north-south orientation across the Plains. The northern terminus of the stationary front turned northwestward over the Dakotas. Some light rainshowers were detected moving northeastward across portions of Minnesota and northwestern Wisconsin.
The center of the high should continue drifting to the east, reaching a position over the St. Lawrence Valley near Montreal, QB on Tuesday morning. The stationary front should slowly shift southward and become positioned along the Gulf Coast.
SNOW REPORTED IN THE CASCADES -- Cold air moved into the Pacific Northwest behind an eastward advancing cold front. As of Monday night, this cold front extended from a low pressure center in northern Saskatchewan southwestward across the northern Rockies and into the Great Basin before terminating in western Nevada. A low pressure system had developed along the front over central Montana to the east of the Divide near Great Falls, with a weaker low pressure area located over extreme southern Idaho.
Thunderstorms moved northward along the front, crossing the Great Basin. A rare severe thunderstorm with large hail was reported near Seattle, WA. Locally heavy rains accompanying these storms caused some flash flooding. A variety of urban and small stream flood advisories, flash flood watches and warnings were issued from Arizona northward across Utah. Strong winds accompanied the strong pressure gradient on either side of the front, as well as with the thunderstorms. Various high wind advisories and wind warnings were issued across Montana and Idaho.
An impressive temperature contrast was found across the front, as high temperatures across Montana to the east of the front reached into the 90s, while to the west of the front, highs across interior Washington State and Oregon were in the upper 60s and low 70s. Cold air brought into the Pacific Northwest caused snow to fall across the Cascades at elevations of about 6500 feet above sea level.
By Tuesday morning, the front should continue movement toward the east, reaching eastern Montana, western Wyoming and central Utah. The low center is expected to move northward along the front into the southern Prairie Provinces. Frost warnings were issued for the valleys of interior Oregon east of the Cascades for Tuesday morning, as temperatures are expected to drop to the upper 20s and low 30s.
TEMPERATURE EXTREMES IN THE LOWER 48 -- The lowest temperature on Monday was 32 degrees at Truckee, CA, while Monday's highest temperature was 115 degrees at Death Valley, CA.
ALASKAN WEATHER -- Clouds covered much of the state on Monday, with exceptions of the interior. Rain fell during the day along the south coast from the Alaska Peninsula east to the vicinity of Prince William Sound. Barrow continued to report snow for the fourth consecutive day. The clouds and precipitation were the result of several systems. A major storm system moved eastward from the Bering Sea and as of Monday afternoon, it was located over the eastern Aleutians. A warm front extended eastward from the low pressure center across the western end of the Alaska Peninsula and then southward into the north Pacific. A second, but weaker, low pressure system was located in the Gulf of Alaska south of Prince William Sound. A stationary front remained over the northern portion of the state.
The state lowest temperature on Monday morning was 18 degrees at Chandalar Lake. The highest temperature across Alaska as of midafternoon on Monday was 65 degrees at Northway.
HAWAIIAN WEATHER -- A large high pressure cell was slowly drifting eastward across the north central Pacific well to the north of Hawaii on Monday. The difference in pressure between the center of this ridge of high pressure and lower pressure over equatorial waters has generated brisk northeast trade winds, that range in speed between 15 and 30 mph. During the day abundant sunshine should be available, with brief passing showers.
Small craft advisories continued in effect for island waters. Ocean swell was expected to arrive along south shores of the islands late Monday night, possibly resulting in the issuance of high surf advisories for surf with heights of 6 feet or greater.
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.