DATASTREME DAILY SUMMARY

Monday 17 September 2001


00Z Weather Systems


WEATHER OVER THE WEEKEND -- Several major weather stories dominated the weather across the country over the weekend, to include Florida's encounter with Tropical Storm Gabrielle, unseasonably cool weather spreading southward across the East and the strong to severe thunderstorms across portions of the Plains and the Intermountain West.

Tropical Storm Gabrielle made landfall on Florida's Gulf Coast near Venice on Friday morning. The bands of thunderstorms accompanying this storm spawned some tornadoes, generated some high wind gusts and produced prodigious amounts of precipitation. As a result, more than 500,000 customers lost power and many schools were closed in portions of the Gulf coast and the central Florida. During the day Gabrielle moved slowly toward the northeast across the Peninsula before turning south near St. Augustine. By Saturday morning Gabrielle had drifted off the Atlantic Coast near Daytona Beach. At least 4 tornadoes were reported near Cocoa Beach on midday on Friday. Some damage was sustained. Several waterspouts, tornadic vortices over water, were also spotted. Winds gusted to 70 mph at sites, especially when the storm made landfall along the Gulf Coast. As the system moved across Florida, winds weakened to gusts of approximately 60 mph. This system was a heavy rain producer, with some locations reporting more than 11 inches of rain. Daily rainfall records were set on Friday across central Florida at Tampa (6.38 inches), Dayton Beach (3.02 inches), Orlando (2.24 inches) and Melbourne (2.04 inches). Several rivers in Florida remained at or above flood stage late Sunday night. This tropical storm contributed significantly to the ending of the extended drought conditions that Floridians endured well into the summer.

Gabrielle continued moving toward the northeast across the western North Atlantic well to the south of the Carolina coast on Saturday and Sunday. As the storm moved toward the northeast on Saturday, northeasterly and northerly winds circulating around the western portions of the storm produced heavy surf and rip currents along the Atlantic Coast from the Carolinas southward to South Florida. After appearing to have gained midlatitude characteristics due to its proximity to a midlatitude stationary front, Gabrielle intensified over the warmer waters of the Atlantic into the third hurricane of the 2001 Atlantic hurricane season when maximum sustained surface winds reached 75 mph. (See more in Eye on the Tropics below.)

A Canadian air mass associated with a large high pressure system over the western Great Lakes on Friday morning spread cool air across the Midwest and into the Northeast. Morning low temperatures in some portions of the northern Great Lakes and New England fell to the low 30s or upper 20s. Afternoon high temperatures across the northern portion of the country extending from the plains of eastern Montana eastward to New England and southward into the Ohio Valley were well below the average highs for mid September, with some temperature departures ranging from 10 to 15 degrees below average. Afternoon temperatures were also held down across the Southeast as a result of the clouds and rain associated with Tropical Storm Gabrielle. Tampa could only reach a high temperature of 73 degrees, which established a low high temperature record for the date. A band of slow moving rainshowers and embedded thunderstorms just behind an eastward moving cold front continued across New England and the Middle Atlantic States. This precipitation that continued through much of Friday morning in the New York City metropolitan area made recovery operations difficult at the site of last Tuesday's terrorist attack.

This high drifted slowly to the south and east on Saturday. Weather conditions improved across the Northeast. The cool air moved southward to the vicinity of the Gulf Coast where the southward advancing portion of the cold front stalled. A daily low temperature record was tied at Mansfield, OH (42 degrees). High temperatures on Saturday were on the order of 10 to 15 degrees below the average highs across the central and northern Plains, as well as along the coastal regions of the Southeast where clouds from Gabrielle kept temperatures suppressed. Sunday morning was a repeat of 24 hours earlier, with low temperature records were tied or set on Sunday at Bristol, TN (42 degrees), in Georgia at Augusta (49 degrees) and Savannah (54 degrees) and in Florida at Jacksonville (57 degrees), Lakeland (65 degrees), Orlando (66 degrees) and Clearwater (67 degrees).

Farther west, a large area of rain and thunderstorms continued to develop and move eastward from the eastern slopes of the Rockies out onto the Plains on Friday. This precipitation was along and to the north of an area of low pressure that developed upon a stationary front, which stretched across the Plains and the northern Rockies. Some of the thunderstorms became severe. Two short-lived tornadoes were reported in southwestern Kansas on Friday evening. A funnel cloud was spotted near Lander, WY. Large hail, with diameters to as large as 1.75 inches in diameter, were reported across southern Wyoming, northeastern Colorado, western Nebraska and western Kansas. Hastings and Kearney in southern Nebraska received record rain totals on Friday with 3.65 and 1.21 inches, respectively. Flash flooding was reported in the vicinity of Lander, WY, where the roof of a nursing home collapsed, probably due to the excessive weight from the rain and hail accumulation. Additional rain and thunderstorms were also reported across southern portions of Arizona, New Mexico and west Texas.

The low pressure area remained across southwestern Kansas on Saturday. Some thunderstorms produced strong winds that had gusts to at least 60 mph and caused wind damage near Lawton in southwestern Oklahoma and large hail near Colorado Springs and Akron in Colorado. There was little movement of the low pressure system and accompanying frontal zone on Sunday. Thunderstorm winds downed trees and utility lines in the Texas Panhandle and southwestern Oklahoma late Sunday afternoon and early evening. Large hail was also reported in the Texas Panhandle near Amarillo, in southeastern Colorado near Pueblo and in southeastern Nebraska. The heavy rains also produced flash flooding, which swept some vehicles off the road north of Amarillo. Farther north, Pierre, SD received a daily record 0.80 inches of rain on Saturday.

Only the Pacific Northwest experienced warmer than average high temperatures over the weekend . On Friday highs across the region were on the order of 10 to 15 degrees above the average highs, while on Saturday, the region of above average high temperatures extended across the portions of the Great Basin.

A weak low pressure disturbance moved onshore across northern California on Friday bring widely scattered showers across the region. This area of precipitation continued into Saturday and Sunday.

Elsewhere, at least one distant tornado was spotted near Snowflake in east central Arizona on Sunday morning.

WEATHER FOR THE START OF THE NEW WEEK -- The following highlights of the national weather have been extracted from the surface weather map for late Sunday night.

High pressure continued to dominate the Midwest and the Eastern Seaboard as the center of the high was positioned over the lower Great Lakes on Sunday night. Relatively clear skies and weak winds were reported from Michigan eastward to New England and southward to Florida. This high pressure system is expected to drift toward the east on Monday, forming an elongated ridge of high pressure extending along the spine of the Appalachians.

Thunderstorms and rainshowers were moving eastward from the Plains into the mid-Mississippi Valley. Some of the heaviest thunderstorms were found to the north of a trough of low pressure and a nearly stationary front that extended eastward from the Front Range of the Colorado Rockies to near Kansas City, MO. The bulk of these thunderstorms stretched from northeastern Kansas across southeastern Nebraska, northwestern Missouri into northeastern Iowa. Additional thunderstorms were found in the Nebraska Panhandle and across portions of eastern Colorado and southeastern Wyoming. In the warmer and more humid air to the south of the front, thunderstorms were found across portions of northeastern Oklahoma, the Texas Panhandle and across the southern mountains of New Mexico to the south of Albuquerque.

A low pressure center is expected to develop along the stationary front over eastern Kansas on Monday and then move toward the northeast, reaching southeast Iowa by evening. As this storm develops, the stationary front is forecast to become a warm front that pushes northeastward into central Illinois ahead of the advancing low pressure center, while to the west of the low, the stationary front is transformed into a cold front that moves southward into northern Oklahoma. Because of the relatively slow evolution of this system, heavy rain is expected to continue across portions of the Plains. A large area of southern Nebraska and northern Kansas could see as much as one inch of rain in the 24 hours ending on Monday evening. Lesser amounts are anticipated from northern Colorado to northeastern Wisconsin. Portions of southern Kansas and the Panhandles of Oklahoma and Texas along and to the south of the advancing cold front could experience a slight risk of severe thunderstorms later on Monday.

Widely scattered thunderstorms continued into Sunday night across the Intermountain West, with much of the activity in the vicinity of the Four Corners, across Utah's Great Salt Lake Basin and over the Snake River Valley of southern Idaho. This activity is expected again on Monday with several tenths of an inch of precipitation forecast.

TEMPERATURE EXTREMES ACROSS THE LOWER 48 -- On Sunday, the lowest temperature reported in the continental U.S. was 27 degrees (Fahrenheit) at Whitefield, NH, while Sunday's highest temperature was 109 degrees at Death Valley, CA.

ALASKAN WEATHER -- A strong system moving to the northeast across the western Gulf of Alaska spread clouds, rain and wind across the Alaska Peninsula and Kodiak Island on Sunday afternoon. This low pressure center was located south of Kodiak Island with a front that spiraled outward across the Gulf just off shore of south central and southeastern Alaska. An arctic air mass associated with high pressure located across the Beaufort Sea and northwestern Canada extended westward along the North Slope. To the south of an east-west oriented stationary front, another high pressure center was located over western Canada with a ridge extending northwestward into interior Alaska. This region experienced relatively cloud-free skies. The stationary front stretched from the Norton Sound across interior Alaska into the Yukon Territory near Dawson. A third high pressure system was a ridge of high pressure that extended northward across the central Aleutians. Farther west, a front trailing southward from a low pressure system in Far Eastern Russia stretched across the central Bering Sea and the western Aleutians.

Snow fell early on Sunday at Kivalina. Rain was reported at Kodiak, Valdez, Juneau and Skagway.

The lowest overnight temperature in Alaska as of Sunday was 19 degrees at Snowshoe Lake and the midafternoon highest statewide temperature was 67 degrees at Ketchikan.

HAWAIIAN WEATHER -- Trade winds were beginning to return to the islands on Sunday as a trough of low pressure moved to the west across the tropical Pacific away from Hawaii. This trough was accompanied by showers and occasional thunderstorms that were found across the Aloha State earlier in the weekend. Some lingering rain continued especially across the western end of the island chain. On Monday a ridge of high pressure located to the north of the islands is expected to dominate the weather over Hawaii, with northeast trade winds increasing to between 10 and 15 mph and relatively sunny skies. Some evening and morning trade wind showers should also remain.

Four to eight foot ocean swells moved north resulting in high surf advisories for the south shores of all the islands. Later on Monday swell from a storm near the central Aleutian Islands could raise surf along the north and west shores of the Hawaiian Islands.

EYE ON THE TROPICS -- As of early Monday morning, Hurricane Gabrielle, a minimal hurricane with 75 mph maximum sustained surface winds, was moving to the east-northeast approximately 300 miles west-northwest of Bermuda at 18 mph. Central sea level pressure estimated at 991 mb. Tropical storm warnings were in effect for Bermuda.

Hurricane Felix continued to move toward the Azores on Monday night. As a minimal hurricane with maximum sustained surface winds of 75 mph, Felix was 265 miles southwest of the Azores and moving to the northeast at 13 mph.

Former Hurricane Erin brushed to the south and east of Newfoundland at the end of last week and lost its tropical characteristics by late Friday night in the North Atlantic as it was moving toward the northeast.

In the Eastern North Atlantic, former Tropical Storm Ivo dissipated on Friday afternoon approximately 500 miles northwest of Cabo San Lucas, Mexico.

SO YOU WANT WEATHER DATA? A national network of several thousand weather observation stations continually monitors the near surface weather conditions across the country. You can access essentially current weather data from around your state or the United States from the portion of the DataStreme Homepage marked as State Surface Data-Text. Consult the Monday optional Supplemental Information for additional information as to the data and how you can interpret these data.


HISTORICAL WEATHER EVENTS - 17 September

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, 2001, The American Meteorological Society.