The eastern Pacific Ocean is alive and well with tropical activity and now the Atlantic Basin has its first hurricane of the season which is the latest for the first hurricane in more than one hundred years. Hurricane Isaias is now pulling out of the southwestern Gulf with maximum sustained winds of around 80 mph (category 1). It is likely to intensify during the next 24 hours or so into a category 2 storm with an outside chance of climbing to “major” category 3 status. There can be some weakening in the hours before landfall which is likely to be around early Friday night and somewhere near the Mobile Bay region of the central Gulf coast. After landfall, impacts of Isaias will continue to the Tennessee and Ohio Valleys on Saturday and all the way to the Mid-Atlantic and Northeast US on Sunday where rain is likely and it can be heavy at times. Meanwhile, Tropical Storm Rachel will make a dramatic right turn and bring rain and wind to southern California and northern Baja, and its vast moisture field will push all the into the northern Rocky Mountain States where it may be cold enough to produce accumulating snow. Tropical Storm Simon is likely to become a hurricane and turn into Mexico with its moisture field likely headed to the southwestern and south-central states.
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The tropics are alive and well and we now have a named tropical storm, Isaias, over the southwestern Gulf of America where water temperatures are near 30 degrees (C)...plenty capable of supporting a late season hurricane. TS Isaias is very likely to become the Atlantic Basin’s first hurricane of the season and can hit the central Gulf coast on Friday night or early Saturday...perhaps as a cat 2 hurricane. While landfall is likely to be in the region between southeast Louisiana and the western part of Florida’s Panhandle, all Gulf residents from Texas to Florida should closely monitor this system.
After landfall, the impact from Isaias is likely to continue well to the north of the northern Gulf with its rain shield possibly moving as far as the Ohio Valley, Mid-Atlantic and Northeast US by later in the weekend. Elsewhere on the tropical scene, Hurricane Rachel over the eastern Pacific is currently churning to the west-northwest; however, it will take a drastic turn to the northeast in coming days and head towards the northern Baja California region with impacts on the way for much of the western US including an added contribution to snow in the Northern Rocky Mountain States.
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All in all, this looks like a relatively quiet and dry week for the continental US, but tropical systems may change that in a big way by this weekend or the early part of next week. There are not one, not two, but three tropical systems that will have to be closely monitored in coming days...two in the eastern Pacific and one in the Gulf. The only one of the three systems that is currently named is “Rachel” which is a minimal hurricane in the eastern Pacific that is on a seemingly harmless westerly track during the next few days. After that, however, there are signs that “Rachel” will take a drastic turn from a westerly direction to northeasterly, and this could bring its moisture field into the southwestern US and potentially, well up to the north of there.
The second tropical wave in the eastern Pacific should strengthen in the near term to become a named tropical storm and potentially, it can attain classification as a hurricane. This trailing system is likely to turn into Mexico and ultimately, its moisture field can impact the southwestern or south-central states. Meanwhile, a tropical wave now over the very warm waters of the southwestern Gulf of America can intensify into named tropical storm status and potentially into the season’s first hurricane for the Atlantic Basin as it pushes towards the northern Gulf region by the weekend…and potentially, well to the north of there.
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Ingredients are pulling together for a major rain event across much of the Southwest and Central US during the next few days including an upper-level low combining with vast amounts of tropical moisture associated with the remnants of an eastern Pacific hurricane named “Polo”. Severe thunderstorms can become part of the overall weather pattern as well during the next few days; especially, across portions of Texas and Oklahoma. While much of the Southwest and Central US are drought-stricken and welcome some rainfall, this may be too much over a short period of time potentially leading to flooding issues.
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An early season nor’easter will impact much of the Mid-Atlantic region and Northeast US and likely have its greatest affects on coastal sections where tidal flooding and beach erosion are big concerns. The time period for impact by this developing storm system for the northeastern states will be from Friday night through Sunday…a prolonged event. The combination of strong high pressure centered over southeastern Canada and intensifying low-pressure over the western Atlantic Ocean will result in an extended period of onshore flow along coastal sections leading to the tidal flooding and beach erosion issues; especially, at times of high tide - and a full moon on Saturday won’t help the situation. As the Atlantic low intensifies and slowly pushes to the north, it will become increasingly under the influence of the strong high pressure ridging to its north, and this will lead to a slowdown and then likely a loop back to the coast. Rain and wind will extend inland back to the big cities in the I-95 corridor during the Friday night through Sunday time period.
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The combination of strong high pressure to the north and multiple low-pressure systems to the east will result in a prolonged period of onshore flow along coastal sections from the Delmarva Peninsula to New England. This extended period of onshore flow will increase the chance for tidal flooding at times of high tide right through the upcoming weekend and a full moon on Saturday will not help the situation. Low pressure will intensify over the weekend as it climbs northward over the western Atlantic Ocean and then it’ll run into a brick wall in the atmosphere with strong riding to its north. As a result, the strong low will slow down, perhaps loop back around towards the coast, and produce rain and wind along coastal sections into early next week.
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Temperatures have been consistently peaking well up in the 80’s in recent days along the DC-to-Philly-to-NYC corridor, but there can be quite a change by the middle of next week. An unusually strong “cold air damming” setup is looking likely with deep high pressure centered over southeastern Canada and this could limit temperatures to the 60’s along the I-95 corridor. In addition to the high-pressure system to the north, this scenario will feature a slow-moving frontal boundary zone that will allow multiple low pressure systems to ride along bringing plenty of moisture into the Mid-Atlantic region. And there is the chance that one of these low pressure systems intensifies just off the Mid-Atlantic coastline in “nor’easter” fashion. The bottom line…occasional rain is likely from Sunday into the middle of next week and some of the rain can be heavy at times to go along with much cooler-than-normal temperatures.
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We have now reached rare territory for the Atlantic Basin due to the lack of hurricanes at this stage of the tropical season. In fact, this is the latest time without an Atlantic hurricane during the satellite era which began in 1966 and there is likelihood that one has to go all the way back to 1941 though confidence in the tracking of hurricanes is far less certain in the pre-satellite era. Having said that, an extremely quiet first half of the tropical season does not guarantee an uneventful second half…indeed, there are some signals that activity will pick up later this month.
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The peripheral region of an intense upper-level ridge can often be quite an active area for thunderstorms this time of year and this summer has been no exception. Specifically, the northeastern quadrant of an intense upper-level ridge where northwesterly flow dominates in the overall clockwise circulation around high pressure can often contain numerous bands of thunderstorms, complexes of thunderstorms and even long-lasting lines known as derechos. This “ring of fire” region in the outer peripheral of high pressure with northwesterly flow aloft has been repeatedly showing up this summer extending from the Great Lakes to the Mid-Atlantic and numerous severe weather outbreaks have been the result. A repeat performance is on the table during the next few days with Tuesday, Wednesday and Thursday likely to feature numerous bands of strong-to-severe thunderstorms that will potentially impact the DC-to-Philly-to-NYC corridor.
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Labor Day is still two weeks away and that puts this outlook in the “speculation” phase; however, there are interesting and somewhat consistent signs of an “omega” blocking pattern in the upper atmosphere over North America which is more typical of winter or spring seasons. An “omega” blocking pattern typically features an upper-level ridge sandwiched in between two upper-level troughs and these systems tend to linger for several days. If indeed this pattern unfolds with an upper-level trough centered over the Northeast US, then any chance for sustained heat for summer’s unofficial end would be quite low in that part of the nation. However, if the ridge sets up over the Northeast US then 90+ degree heat would certainly remain on the table in those urban areas along the I-95 corridor.
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