Mesoscale Precipitation Discussion 0831
NWS Weather Prediction Center College Park MD
503 PM EDT Thu Sep 13 2018

Areas affected...Coast and Coastal Plain of SE NC

Concerning...Heavy rainfall...Flash flooding possible

Valid 132103Z - 140303Z

Summary...Heavy rainfall associated with the Central Dense
Overcast of Hurricane Florence will lift westward and onshore
through the evening. Rainfall rates of 2-3" per hour are possible
which may produce flash flooding.

Discussion...Latest radar imagery from KMHX WSR-88D radar shows a
nearly unbroken area of heavy rain with embedded convective
elements northwest of the center of Hurricane Florence. Radar
estimated rainfall rates have been widespread 1-1.5"/hr, and
recent observations show that 3-6" of rainfall has been measured
across the Crystal Coast so far this afternoon. As Florence moves
very slowly to the W/NW through the evening, the heaviest echoes
will continue to rotate onshore producing nearly continuous
torrential rainfall across the threat area.

18Z KMHX upper air sounding showed that PWAT had increased to 2.33
inches, while the blended TPW product has up 2.5 inches just
offshore, positioned to pivot onto the coast. The freezing level
at MHX is approaching 17,000 ft, RAP analyzed MLCape remains
500-1000 J/kg, and maximum lapse rates are less than 6C/km, all
indicators of efficient warm rain processes. 850mb inflow has
reached 85 kts on KMHX VWP, greater than the 0-6km mean wind which
is 70 kts. Inflow wind speeds greater than the mean wind will only
enhance lift through the column and create the potential for
rainfall rates of 2-3"/hr. Individual cells will race to the S/SW,
but training of higher reflectivity is likely as the bands rotate
onshore, and rainfall totals of 3-5" are likely, with 6" or more
possible in some locations, especially along the Crystal Coast.

The threat area has been expanded a bit to the NW from the
previous MPD as CIN has eroded and the column is moistening as
evidenced by a PWAT plume of 2" advecting inland to Interstate 95.
Additionally, higher MLCape of 1500 J/kg is being advected into
the region from the NE, and 0-6km bulk shear has increased to
30-40 kts, which will help persist and potentially intensify some
of the radar echoes as they advect inland. Rainfall further inland
across the coastal plain will overall be less robust, but very
heavy rain rates may still produce flash flooding across this area.

Although antecedent conditions from the past few weeks are dry,
the rainfall that has occurred today has been saturating the
soils. Latest HRRR 1cm soil moisture is over 50% for the immediate
Cape Fear coast and points north, so flash flooding will become
more likely as rains continue.

Weiss

ATTN...WFO...ILM...MHX...

ATTN...RFC...SERFC...

LAT...LON   35487656 35467589 35347542 35127542 34967574
            34877609 34667635 34537655 34587684 34537712
            34397738 34237764 34007790 33787801 33837824
            33927832 34317827 34717804 35107770 35367711