1:15 PM | ***Significant rainfall for the Mid-Atlantic region and a hurricane threat late in the weekend***

[Visible satellite image of Hurricane Joaquin with signs of an "eye" forming; courtesy Penn State/Weather World]

Discussion

A potentially dangerous weather pattern is unfolding for the Mid-Atlantic region that can include very heavy rainfall, flooding and beach erosion along coastal sections over the next few days from the combination of strong “blocking” high pressure to the north and a “nor’easter-like” storm system. In addition, there is the potential for major impacts from Hurricane Joaquin in the Mid-Atlantic region late in the weekend or early next week. Exactly where Hurricane Joaquin makes landfall – if ever – is still in question with some of the most recent model information suggesting North Carolina and others sticking with an "out to sea" solution. However, whether or not Joaquin actually makes landfall in the US, significant rainfall is still likely to occur and NOAA's GFS forecast model continues to predict 5-10 inch amounts in much of the Mid-Atlantic region over the next seven days (shown below).

[12Z GFS total rainfall output for the next 7 days (orange area is 5-10 inches; courtesy NOAA]

Hurricane Joaquin has strengthened slightly in the past few hours with sustained winds now at 80 mph. Joaquin has moved slowly to the southwest during the past several hours, but the shortwave ridge causing this motion will weaken in a day or two as a strong upper-level trough forms over the Southeast US. Once this upper-level trough becomes well-established, the hurricane is likely to turn northward and then “pin wheeling” action around the upper-level low could cause Joaquin to push to the northwest – perhaps right towards the Mid-Atlantic coastline.

[Shear tendency during the past 24 hours; courtesy University of Wisconsin/CIMSS]

As far as intensification is concerned, Joaquin is moving into a region with little or no wind shear (circled area on map above) and over warmer-than-normal waters - all of this should allow further strengthening – perhaps even to category 3 (“major hurricane”) status. Joaquin is likely to reach its lowest pressure in about 72 hours or so and then begin to weaken slowly as it pulls farther up the coast on its way over somewhat cooler waters. Strong “blocking” high pressure will set up later this week across southeastern Canada and this will be a key player in the eventual possible push of Joaquin towards the Mid-Atlantic coastline and also in its slow movement throughout the next several days.

One of the reasons for concern in this unfolding pattern is that there will be a “nor’easter-like” event ahead of a potential strike by Joaquin. Heavy rain and a long-lasting period of strong onshore flow (20-40 mph E-NE winds) will take place in the Thursday-Saturday time period and this would make any potential rainfall from Joaquin late in the weekend or early next week that much more damaging.

Bottom line…all eyes from North Carolina to Long Island should continue to closely monitor this unfolding situation.