Category: General Weather

As much as 10 or more inches of rain fell south of Dallas, Texas on Friday,  resulting in widespread flooding. This occurred as moisture was able to be pulled inland from the Gulf of Mexico along a low level jet that had a strength that was at times 2 to 3 standard deviations above normal. Also, surface moist convergence resided within an area that contained plentiful amounts of moisture in the form of precipitable water that was 2 to 3 standard deviations above normal. This all took place over the same area for most of the day. Additionally a cold front approached from the north and thunderstorm chances rose to the north of the area of convergence. As that cold front approached from the north, upper level divergence occurred in the right entrance region of the upper level jet allowing for large-scale upward motion. Consequently many cells were able to back-build and resided in the same place for long periods of time allowing for an over-saturation of the ground in those places and standing water for flooding.

Moving forward, model projections have plenty more flooding moisture coming into the Southern Plains, but it should remain further south this time. Major Hurricane Patricia, which rapidly weakened, but was above Hurricane status just before reaching landfall in Mexico, will have an effect on the Southern Plains. Patricia’s remnants will get drawn into the aforementioned jet stream and will add moisture to the rainfall along the southern shores of Texas. The upper level jet and its dynamics move away from the region, so the bulk of the precipitation will now be a result of the remnant low pressure system from Patricia. Precipitable waters will be up to 3 to 4 standard deviations above normal, which is higher than what was in North Texas. But, while the storm should have heavier rainfall rates with strong low level winds bringing more moisture in from the Gulf, a short time for precipitation occurrence will happen as the low pressure system moves away quicker than the stalled out boundary in North Texas. A severe weather threat also exists with increased shear paired with the strong moisture content. Generally, tornadoes occur in the right front quadrant of a low pressure system depending on the direction of movement because that is where the apex of the low level jet tends to be. So, a northward movement would allow tornadoes to occur in the northeast side of the low pressure system. The strong rain should be out of Texas by Monday morning. As the storm continues along, it will continue losing tropical characteristics and will move to the northeast and affect regions from the Gulf-bordering States to the Northeast through the middle of next week as the energy and moisture from Patricia combines with another trough to the north and swings to the north and east.

Speaking of previous tropical cyclone Patricia, there are only two named storms, including Patricia, from the Central Pacific to the Atlantic Ocean. As of late Saturday afternoon the remnants of Patricia were located about 45 miles southwest of Monterrey, Mexico. A low pressure system over southern Texas is also developing, but is expected to be non-tropical even with the remnants of Patricia being absorbed into it. The main threats continue to flooding and mud slides in Mexico and flooding and severe weather in Texas.

After a relatively warm summer and early autumn, some of the coldest air so far this season will sweep southward from Canada over the next several days.

A cold front will drop southward across the Plains and the Great Lakes on Thursday with a large high pressure area building in southward behind it. Scattered showers are expected ahead of the front, but they will be mainly light. The bigger story will be gusty northwest winds behind the front ushering the cooler air into the region. Frost Advisories and Freeze Watches have already been posted for Friday morning across portions of Nebraska, Kansas, and eastern Colorado, and more will likely be issued.

As the front marches eastward Thursday night and Friday showers will spread into the Northeast while the cold air pours into the Midwest. Rain could mix with some wet snow before ending across portions of northern Minnesota and the Upper Peninsula of Michigan. As high pressure builds in, skies will clear out across parts of the area and winds will diminish, allowing temperatures to drop into 20s and 30s across much of the Midwest. While a frost or freeze has occurred across northern parts of the region already, in southern areas, this will lead to an end of the growing season.

By Friday night the front will push offshore, but an upper-level low pressure area will settle into the region. This will likely trigger additional showers across parts of the Eastern Great Lakes and northern New England. Most of these will be light once again, but with colder air settling in, some wet snow could mix in, especially in the higher elevations of northern New England. Little, if any, accumulation is expected, except at the higher peaks. With the upper-level system nearby, Saturday will be a breezy and cool day across much of the region under partly sunny skies. As this system moves into southeastern Canada, high pressure will build into the Great Lakes, allowing skies to clear out. This may result in frost and/or freezing conditions across most of the Ohio Valley, the Appalachians, and interior Northeast, ending the growing season across much of the region.

By Sunday, high pressure slides eastward, allowing for a sunny but cool day across most of the Northeast. The exception will be across northern New England. With the upper-level low still nearby, rain and snow showers will continue across the higher elevations of Vermont and New Hampshire, as well as much of northern and western Maine. Accumulation of 1 to 3 inches are expected, with some heavier amounts possible in extreme northern Maine. Skies should become clear across most of the region Sunday night, and with diminishing winds, temperatures will drop quickly at night. A widespread frost and/or freeze is expected across much of New England, mainly away from the coastal plain. Temperatures may only drop into the middle 30s in the urban areas, but most of the suburbs will likely drop into the 20s to lower 30s by Monday morning.

As the high slides offshore, southwest to west winds will allow warmer air to move back in, with high temperatures bouncing back into the 60s and lower 70s by the middle of next week.

A low pressure system will move through the Northern Plains this weekend and into Monday with strong gusty winds. Sustained winds strong as 30 to 40 mph with gusts up to 50 mph  or more are possible into Monday in places such as Jamestown, North Dakota. One other factor that could help to exacerbate this even further is the fact that some areas, especially to the north, may see some rain from the low pressure system. Often winds get briefly stronger in rain as even stronger winds aloft would get brought down to the surface. Winds should die down in the Northern Plains late Monday into Monday night as the low pressure system and attendant cold front leaves the area.

It was a chilly weekend across the Northeast as Frost Advisories were issued over Southern New England Saturday night as dry air poured into the region behind Friday’s cold front. With the cold and dry air in place, radiational cooling allowed low to drop into 30s in many areas. Radiation cooling occurs where warmer air can escape readily into the upper atmosphere and cool more completely than if there were clouds around. Of course the urban heat island effect, elevation, proximity to warmer land masses like the ocean and soil type play a huge role helping to regulate how cold temperatures get.  For eastern areas of Massachusetts and eastern areas of New York, that recorded frost, this is right around the normal date for their first frost, which is around October 11-20. Western Massachusetts areas are only a day or two late with their first frost normally from October 1-10. Overall though, it is well on target with the average first frost. Temperatures should be on a warming trend ahead of Tuesday’s cold front.

In the tropics, the Atlantic region does not have any areas that are being monitored for tropical development, but the Pacific Ocean has Tropical Storm Nora. It crossed from the Eastern Pacific into the Central Pacific Saturday evening. Nora currently has maximum sustained winds around 65 mph. Satellite images showed a developing eye wall aloft. In the early part of its forecast, as it continues its westerly track, shear will remain low and warm waters around the storm will allow for further strengthening. By Tuesday, the westward trek of the storm will be changed to more northerly as a high pressure system to the north begins to break down and an area of low pressure approaches from the west. The northerly track would start to occur well east of the Hawaiian Islands. As Nora begins its turn north on Tuesday, an area of low pressure will also allow vertical shear to increase so a decrease in strength may occur after Monday and along its northerly track. The other area being monitored is currently centered about 600 miles south of Acapulco, Mexico. Environmental conditions are expected to be conducive for slow development and a tropical depression is likely to form late this week as it continues along its westward track.

Historic rainfall has fallen across portions of the Southeast and Mid-Atlantic states over the past few days. Unfortunately, the combination  of strong onshore winds, a convergence boundary and tropical moisture from offshore Hurricane Joaquin will produce even more rainfall into Monday. From start to finish, some places in the Southeast could see up 15 to 20 or more inches of rain from this event. In South Carolina, the 24 hour record for rainfall is 14.88 inches. Strong winds have been another piece of this storm, but not as noteworthy as the rain and flooding. There were numerous reports of trees down while wind gusts were between 35 and 45 mph in North and South Carolina Saturday morning.

In the Atlantic, Hurricane Joaquin is moving to the north-northeast at 14 mph, past Bermuda where its eye has begun to appear on the Bermuda radar. It is expected to pass around 70 miles west of Bermuda and the latest aircraft recon report showed a wind of close to 110 mph in the storm. Two different systems will help define the flow for the storm’s movement over the next few days as a low pressure system to the west and a high pressure system to the east allow for a north-northeast path, with a turn more toward the northeast expected on Monday. Then, an acceleration to the east-northeast is forecast, taking it away from the United States. Along its track, it will encounter increasing shear over the next two days while the environment becomes increasing drier. With these in mind, a decrease in intensity for the storm is forecast for the next 48 hours. After that, an extratropical transition is expected to occur by the middle of the week, allowing for further weakening as it reaches an area of very strong shear and cooler water temperatures.

Two other areas warrant watching in the Atlantic. One is several hundred miles southwest of the Cape Verde Islands and has a large area of disorganized showers and thunderstorms. Upper level winds are not conducive at the moment, so any development this week would be slow at best. The second is even weaker than the first, and is located about 800 miles east-southeast of Bermuda. Environmental conditions are becoming less conducive for development with Hurricane Joaquin nearby. Therefore, development of this system is not anticipated.

The Eastern Pacific contains the tropical system that is the biggest threat to the United States. Tropical Storm Oho is located about 565 miles south-southeast of Honolulu, Hawaii, or 375 miles south of South Point, Hawaii. It is drifting toward the north at just 2 mph, and has maximum sustained winds of 40 mph. A turn to the north and then northeast with an increase in forward speed is expected on Monday and for the foreseeable future as a high pressure system to the north breaks down and allows for more southwesterly steering flow. The storm will be fighting through shear, but will have warm sea surface temperatures to tap into, ahead of stronger shear towards mid-week, which should lead to a weakening trend. Farther to the west, Tropical Cyclone Eight-C has become post tropical about 450 miles south-southwest of Johnston Island. It has sustained winds of 30 mph and is moving northwest at 3 mph. The remnants of this system are expected to head out over the open waters of the Central Pacific Ocean.

The past several months have been mostly warm and dry across much of the Northeast. The next week or so will see a continuation of the dry pattern, but temperatures will be much cooler. Meanwhile, persistent but much-needed rainfall is expected across the Southeast for the next several days.

A large area of high pressure will settle into southeastern Canada over the next several days, slowly drifting east-southeastward into New England and then into the North Atlantic. This will provide plenty of sunshine to much of the Northeast. However, the clockwise flow around the high will produce northeast to easterly winds across the region, blowing in off the Atlantic, where water temperatures are only in the upper 50s to middle 60s. As a result, high temperatures will only be in the 60s to lower 70s for most of the remainder of the week. In most cases, this is near to a little below normal for the latter half of September. Nighttime lows will be mainly in the 50s near the urban areas and 40s in the suburbs, with some 30s in northern locations. This is also a little below normal. This is a stark contrast to the first half of September, which was close to the warmest on record for much of the region.

The dry weather is not good news though, as much of the Northeast has been in a drought for the past several months. Many locations are 4-8 inches below normal over the past several months. This may have a big impact on the fall foliage across the region. The warm and dry conditions may result in less vibrant colors across the region, and may also result in many leaves falling from the trees before reaching peak color. Windy conditions could result in additional leaves dropping early as well. Some of the leaves are already starting to change colors in far northern areas, with a few splashes of color showing up elsewhere.

Meanwhile, to the south, a weak area of low pressure is sitting a few hundred miles off the North Carolina coastline. With the large high pressure area to the north, the system has nowhere to go, and will likely remain off the coast for the next several days, slowly drifting westward towards the Carolinas. Although water temperatures remain warm, the system is not tropical in origin, and conditions aren’t favorable for much strengthening. The storm will bring plenty of beneficial rainfall to the region though, with widespread totals of 1-3 inches expected from southern Virginia across the Carolinas and into Georgia. Along the coast of North and South Carolina, even heavier totals are possible, with some places possibly receiving more than 5 inches of rain by the end of the week.

In between the high to the north and low to the south, an area of persistent strong winds is expected along the Mid-Atlantic coastline. Easterly winds of 15 to 25 mph, occasionally gusting to 40 mph or more are expected for much of the week from New Jersey southward to North Carolina. When combined with astronomically high tides, some coastal flooding is possible. Coastal flood advisories and high surf advisories have already been posted for parts of the region, and additional advisories and/or warnings are likely to be issued in the next day or two. There is also a high risk of rip currents in this area, so anyone planning on heading to the beach should pay attention and heed any warnings posted.