WELCOME TO ONLINE WEATHER STUDIES - The Daily Weather Summary file will describe the current weather pattern across the U.S. Additional Supplemental Information Files will provide optional background material, when appropriate.
WELCOME TO SEPTEMBER -- Today is the first day of meteorological autumn, the three-month (September, October, November) interval that meteorologists frequently use for record keeping processes. Additional information will be presented in the next several weeks concerning meteorological seasons and the astronomical seasons, such as the familiar autumn that begins on the autumnal equinox in three weeks. The name September appears to be derived from "Septem", the Latin word for the number seven, representing the seventh month of the year in the old Roman calendar that started with the month of March.
DENNIS TO MAKE A RETURN CALL? On Wednesday Hurricane Dennis began to slow as it moved toward the east-northeast away from the North Carolina Coast, carried along initially by the southwesterly steering winds. By late afternoon, these winds had shifted and the presence of a large high pressure system over the Northeast caused Dennis to reverse direction at a point roughly 150 miles east of Cape Hatteras, NC, and begin to drift slowly toward the west at 3 mph. Late on Tuesday night, Hurricane Dennis was downgraded to Tropical Storm Dennis as sustained surface winds fell below the 75 mph minimum for hurricane status to 70 mph. At that time, Dennis was located approximately 105 miles east of Cape Hatteras and moving to the west at 4 mph. Central pressure was 987 mb (29.15 inches of mercury). Onshore winds generated heavy surf and a storm surge of as much as 4 feet above high tide, producing flooding along the barrier islands and sounds. A long shore ocean current also contributed to the beach erosion. Heavy rainfall continued along the Grand Banks of North Carolina.
The forecast was for Tropical Storm Dennis to continue moving to the west during the overnight hours, then possibly turn toward the southwest, to parallel the coast on Wednesday. While this system is expected to weaken, some increased winds could occur as Dennis returns into the warm waters of the Gulf Stream. A hurricane watch was issued Tuesday evening for the coast from Cape Lookout, NC, to Chincoteague, VA, to include Pamlico and Abermarle Sounds, as well as southern Chesapeake Bay. This watch means that the potential for hurricane with winds in excess of 75 mph could affect the area within 36 hours. Essentially the same area remained under a tropical storm warning, with winds between 39 and 74 mph anticipated within the next 24 hours.
Strong onshore winds -- in part from the circulation around Dennis and in part from the large pressure gradient (or difference in pressure) between the large high pressure cell over the Northeast and Dennis -- continued to produce high seas from Virginia north to New Jersey. Heavy surf advisories were in effect for the coasts of the Delmarva Peninsula and New Jersey, and coastal flood warnings were posted for portions of the Delaware and New Jersey coasts, especially in the vicinity of Delaware Bay and Cape May, NJ. Gale warnings were also in effect north of Chincoteague to Fenwick Island, DE for winds up to 74 mph generated by the tight pressure gradient.
A COOL START ACROSS THE SOUTHEAST -- The Canadian high pressure system that has brought the first hint of autumn-like conditions to the Northeast at the start of the week continued to drift slowly east-southeastward on Tuesday. The center of this sprawling high pressure system was located over the northern Adirondacks of Upstate New York on Tuesday night. The air mass associated with this system spread southward across the Southeastern States, essentially reaching the Gulf Coast. The ingredients of low humidity, relatively clear skies and weak winds associated with the Canadian high pressure were once again conducive for significant night time cooling. Numerous record low temperatures were either tied or set Tuesday morning across the Southeast to include Elkins, WV (39 degrees); Morgantown, WV (46 degrees); Asheville, NC (49 degrees); Augusta, GA (55 degrees); Huntsville, AL (59 degrees); Savannah, GA (61 degrees) and Downtown Charleston, SC (66 degrees). Despite of cool conditions across the portions of the Southeast, Tampa, FL had a record high low temperature on Tuesday morning with 80 degrees. While the nighttime hours were cool across a large portion of the East, sunny skies during the day permitted temperatures to rise fairly rapidly.
By Wednesday morning, the major center of the high is anticipated to be centered over the upper Connecticut Valley between Vermont and New Hampshire. Additional high pressure centers could extend across the southern Appalachians into western North Carolina.
ACTIVE WEATHER IN THE PLAINS AND WESTERN GULF COAST -- Warmer air was returned to the central portion of the country on Tuesday, brought northward by the southerly winds that formed part of the clockwise circulation about the western flank of the large high pressure cell over the Appalachians. A cold front along an elongated trough of lower pressure approached from the northwest, to help draw a southerly wind flow northward across the region. Daytime temperatures have been reaching the 90s across the Plains. Some locations remained relatively warm even overnight. The overnight low at Denver, CO fell to only 66 degrees, tying the record high minimum temperature for the date.
The onshore flow of warm, humid Gulf air across the Texas and Louisiana Gulf Coasts lead to some active thunderstorms. Severe thunderstorms were reported across the Mississippi Delta, and near Houston, TX. A thunderstorm downburst -- a rain-laden downward gush of air -- was reported to have been responsible for the collapse of a building under construction in Houston on Tuesday evening. Winds gusting to 60 mph were also reported to have caused other damage in the metropolitan area.
As of Tuesday night, the cold front extended southward from a low in western Manitoba to the Black Hills of South Dakota before turning southwestward. A weak low pressure system was located along the front over Wyoming. Thunderstorms were found along the front, across the Dakotas the Nebraska Panhandle, Some of these had become locally severe, with large hail and strong winds.
The cold front should continue to move eastward across the Dakotas and western Nebraska before dawn on Wednesday. As result, the eastern Dakotas continued under a slight risk of severe thunderstorms associated with this cold front through Wednesday morning. During the day on Wednesday this risk area should shift to southwestward over northeast Colorado, in the vicinity of the weak low pressure center.
COOL WEATHER PUSHES INTO THE NORTHWEST -- A cool high pressure continued to move into the Pacific Northwest in the wake of the cold front that moved eastward across the Northern Rockies on Monday and early Tuesday. Except for some lingering showers in the Puget Sound region of western Washington State, much of the region cleared. However, on Monday the cold pool of air that moved onshore, coupled with clouds and rain, held the high temperature on Monday afternoon at Pendleton, OR to 58 degrees, setting a record low high temperature for the date and also for the entire month of August. By Tuesday morning, numerous low temperature records were set over the region as a result of the high pressure, with relatively clear skies, weak winds and the lack of a strong onshore flow that would bring moderating temperatures in from off the Pacific Ocean surface. At Burns, OR the overnight low temperature fell to 24 degrees, setting a new record low temperature for the date, and tying the record low for the month of August. Other records included Klamath Falls, OR (31 degrees), Yakima, WA (37 degrees), Crescent City, CA (43 degrees ) and Eureka, CA (45 degrees). The 45 degree low at Eureka tied for the second lowest temperature ever recorded during the month of August. Some light snow was reported on Tuesday at Mullan Pass (6100 foot elevation) in the Bitterroot Mountains between Montana and Idaho.
Frost warnings were posted on Tuesday for portions of northern California, interior and northeast Oregon as temperatures are expected to fall with the passage of the high pressure cell eastward overnight.
YESTERDAY'S TEMPERATURE EXTREMES ACROSS THE CONTINENTAL US --Tuesday morning's lowest temperature was 22 degrees at Burns, OR, while the highest temperature on Tuesday was 107 degrees at Borrego, CA.
ALASKAN WEATHER -- A strong storm system located over southeastern Bering Sea on late Tuesday afternoon produced widespread clouds, rain and windy conditions along the eastern Aleutians, Bristol Bay, the Pribilof Islands and the Alaska Peninsula. A frontal boundary that stretched from the low center across the Alaska Peninsula to near Kodiak Island earlier in the day had begun to dissipate, remaining as a trough line. Cold Bay had southeast winds with gusts to 50 mph, while St. Paul Island and Dutch Harbor had gusts to as high as 40 mph. Farther to the east, some light rain was reported along the north Gulf coast, near Prince William Sound. A stationary front remained stretched across the state, near the Arctic Circle.
The state lowest overnight temperature on Tuesday morning was 28 degrees at Ugnu Kuparuk. The highest temperature by mid afternoon of Tuesday was 67 degrees at Merrill Field.
HAWAIIAN WEATHER -- A large ridge of high pressure remained to the north of Hawaii on Tuesday and continued to produce strong easterly winds across the islands. These winds from the east were stronger than the typical easterly trade winds that are usually found across the tropical and subtropical oceans. In addition, rainshowers increased in intensity over the windward slopes of Maui and the Big Island. This weather pattern is expected to continue through Thursday as the high pressure cell to the north is anticipated to remain relatively stationary. Small craft advisories remained in effect. High surf advisories were posted early Tuesday morning for the south shores of the islands as the ocean swell approached from the south.
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.