Cooling Out West Slightly

General Overview: HEAVY RAIN AND FLASH FLOODING THREATS CONTINUE ACROSS THE EASTERN SEABOARD AND SOUTHWEST TODAY AND TOMORROW AS TROPICAL STORM IMELDA SLOWLY APPROACHES THE SOUTHEAST COAST. MIXED PRECIPITATION ACROSS THE PACIFIC NORTHWEST AND NORTHERN ROCKIES. ABOVE NORMAL TEMPERATURES WILL DOMINATE THE NORTHERN PLAINS AND UPPER MIDWEST THROUGH THE FORECAST PERIOD.

EAST:  An active weather pattern will impact the Eastern United States over the next several days. Impacts from Tropical Storm Imelda are expected from the eastern Florida Peninsula into the coastal Carolinas. Heavy rain, flash flooding, and life-threatening rip currents can be expected across these areas through Tuesday before Imelda turns northeast and begins moving out into the open Atlantic. Improving conditions are expected inland around the middle of next week as high pressure builds across the Northeast. Rain will gradually diminish across most eastern areas by late next week as the tropical system moves away from the coast. The Gulf Coast will continue to see rain and thunderstorm activity through much of the period.

Temperature Anomalies:

-Days 1-3: Generally near to slightly above normal temperatures across most of the Eastern region, with the warmest anomalies (3-6°F above normal) in the Northeast.

-Days 4-6: Near normal temperatures for most areas, with slightly cooler conditions possible along the coastal Southeast as cloud cover and precipitation from Hurricane Humberto impacts the region.

-Days 7-10: Warming trend developing with above normal temperatures spreading across the Northeast and Mid-Atlantic, with anomalies of 3-6°F above normal.

CENTRAL:  High pressure will initially dominate across portions of the Central Plains, providing relatively quiet weather. A frontal boundary will develop and push through the Great Lakes and Upper Midwest by midweek, bringing a chance of showers and thunderstorms. The most significant feature will be the persistent above-normal temperatures across the Northern Plains and Upper Midwest, where temperature anomalies will be well above seasonal norms. Southern portions of the region will see scattered rain and thunderstorm activity, particularly near the Gulf Coast. Low pressure developing in the Northern Plains by late week will bring additional precipitation chances to the region.

Temperature Anomalies:

-Days 1-3: Significantly above normal temperatures across the Northern Plains and Upper Midwest with anomalies of 6-12°F above normal. Near normal temperatures for the southern portions of the region.

-Days 4-6: Continued well above normal temperatures across the Northern Plains and Upper Midwest with anomalies reaching 10-15°F above normal in some locations, particularly in North Dakota, South Dakota, and Minnesota.

-Days 7-10: Above normal temperatures persisting across the Northern Plains and Upper Midwest, gradually moderating but still 6-10°F above normal. Near normal temperatures returning to southern portions of the region.

WEST:  An active pattern will continue across the Pacific Northwest and Northern Rockies with rain and mixed precipitation. Several low pressure systems will move through the region bringing periods of precipitation. The Southwest will remain generally dry with high pressure in place. Mountain areas in Idaho, Montana, Wyoming, and Colorado will see periods of rain and higher elevation snow. The Pacific Northwest coast will experience periods of rain, with some thunderstorm activity developing in the interior mountain regions. By late week, a new frontal system will approach the Northwest coast bringing another round of precipitation.

Temperature Anomalies:

-Days 1-3: Near to slightly above normal temperatures for most of the region, with some cooler spots in areas receiving precipitation. The Northern Rockies will see temperatures 3-6°F above normal.

-Days 4-6: Continued above normal temperatures for the interior West and Rockies, with some areas seeing anomalies of 6-9°F above normal. Cooler conditions developing in the Pacific Northwest as new systems approach.

-Days 7-10: Cooling trend for the interior West with near normal temperatures returning to most areas. Some below normal temperatures developing in portions of the Great Basin and interior Northwest with anomalies of 3-6°F below normal.

TROPICAL:
ATLANTIC BASIN:
1. Central Tropical Atlantic: Hurricane Humberto is moving toward the northwest at 14 mph. Humberto is a category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale and has maximum sustained winds of 140 mph. Humberto will continue on a general northwesterly path today before turning north and then eventually northeast by late Tuesday. Humberto will then rapidly accelerate off to the northeast and further out into the open Atlantic by Wednesday. No impacts to the U.S. are expected with this storm system.

2. Southwestern Atlantic: Tropical Storm Imelda is currently over the Bahamas and moving north at 9 mph. Imelda has sustained winds of 40 mph. Imelda will continue to organize and strengthen today as it slowly moves north or north-northwest generally parallel to but just offshore of the Florida Peninsula. Imelda will bring periods of rain, breezy winds, and rough seas to areas along the Florida coastline as Imelda passes nearby. Imelda is expected to become a hurricane by early Tuesday morning as it begins a more northeasterly turn. Fortunately, steering flow and its interaction with nearby Hurricane Humberto will keep Imelda offshore and will even push Imelda farther out to sea by late Tuesday and early Wednesday. Still, its proximity periods of rain, rough seas, and the risk of rip currents will be possible from northern Florida into the Carolinas through Tuesday due to its proximity to the coast. Any impacts from Imelda will dissipate by late Wednesday.

EAST PACIFIC BASIN: 
1. Post-tropical Cyclone Narda currently remains over the open waters of the Pacific Ocean. It will continue a weakening trend through the next 48 hours and eventually dissipate sometime Wednesday. No impacts to the U.S. are expected.

2. An area of disorganized convection is noted well off the southwest coast of Mexico. A slow organization will likely occur through the next several days due to a conducive environment, and a tropical cyclone is likely to form around the middle of the week. Tropical formation chance through 48 hours is medium at 50%, and tropical formation chance through 7 days is high at 80%. No immediate concerns to land are anticipated, although DTN will monitor the latest forecast for any changes.