Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 291017

Area Forecast Discussion
National Weather Service Raleigh NC
615 AM EDT Sun May 29 2016

.SYNOPSIS...Tropical Storm Bonnie will approach the South Carolina
coast this morning, and then track very slowly northeastward along
the coast of South Carolina and North Carolina through the middle of
the week.


.NEAR TERM /through Monday night/...
As of 305 AM Sunday...

For today: Thickening clouds and rising rain chances are on the
horizon for central NC today. The center of TS Bonnie is now located
a couple hundred miles south of MYR and is on pace to reach the
central SC coast near CHS later today, before essentially stalling
out. Convection with Bonnie remains disorganized and has frequently
been focused well away from its center, and this should remain the
case today despite expected minor strengthening. Water vapor imagery
reveals the stream of deep moisture east and north of Bonnie,
extending from NE of the Bahamas to the NW across NC. Low level mass
convergence occurring now along the southern NC and NE SC coast is
supporting a broad band of steady showers, and this should continue
to track to the NW through central NC this morning. The mid level
shear axis which has extended across SC and SW NC over the last day
or two will pivot slowly to the ENE through tonight, leading to
increasing DPVA in central/eastern NC. One vorticity center in
particular over central/SE SC will streak NNW then N into our area
later today into tonight, while a second potent mid level vorticity
max now located well east of SAV and east of the Bonnie center
shears to the NNW over eastern NC late tonight. Both of these
features combined with the influx of deep moisture (PW nearing 2.0")
and added lift from weak upper divergence will support likely to
categorical pops today, slipping gradually after nightfall to likely
areawide mid-late evening, then to chance west / likely east late
tonight with decreasing coverage / intensity as the weak yet
vertically juxtaposed lift mechanisms start to shift into eastern
NC/SE VA. Forecast instability is modest, peaking near 1000 J/kg
mainly east of the Triad, with marginal deep layer shear barely
reaching 20 kts, so will restrict a mention of isolated thunder to
the afternoon and early evening hours in eastern sections, mainly
east of Highway 1, where surface dewpoints at or above 70 will
contribute to the instability potential. Temps are tough today as
any break in the clouds and subsequent heating (a likely bet in the
eastern CWA) will cause temps to soar. Conversely, the lighter but
more expansive rain now over the western Piedmont (supported by
moist upglide at 300K-315K) in tandem with the NW movement of the
coastal rainband inland should keep lots of clouds and good rain
chances there, hindering heating. Thus, expect highs from the lower
70s far NW to the lower 80s over the Coastal Plain. Despite the
steady slow decrease in pops from west to east tonight, chances will
remain higher than climo, especially in our eastern half, and clouds
will be abundant and at multiple levels, cutting down on nocturnal
cooling. Total rainfall through tonight is expected to range from a
half to one inch, although certainly there will be locally heavier
totals, given the slow MBE movement. lows from 64 west to around 70

Mon/Mon night: While this Memorial Day is shaping up to be wetter
than a typical spring day especially in the east half, the details
unfortunately remain murky. The weak shear axis still sitting over
the region will pivot to a more north-south orientation Mon,
eventually leading to weak NVA over the western Piedmont by Mon
night, as the center of Bonnie continues to sit and spin with a very
slow northeastward drift over the central and northern coast of SC.
The streak of high-PW air (1.5-2.0") into the eastern half of NC
(along an inverted surface trough extending NNE from Bonnie`s
center) continues into early Mon, but wanes through the day and
night as the band of greatest and deepest moisture flux shifts to
our north, while mid level winds to the NE and E of Bonnie veer from
SE to more southerly as the shear axis lifts out. So while rain
chances should be lower than today, they`ll remain higher than
climo, especially east. Pops will range from 30-40% west to 60-70%
east on Mon, tapering down to 20% west ranging to 30-40% east Mon
night with loss of heating and departure of large scale mechanisms
to force ascent. Highs from around 80 to the lower 80s with mostly
cloudy to cloudy skies. Lows Mon night in the mid to upper 60s. -GIH


.SHORT TERM /Tuesday through Wednesday night/...
As of 245 AM Sunday...

Tropical Storm Bonnie and its remnants will be the main weather
story during the short term forecast period. With very weak flow
aloft there will not be much to steer the storm away from the
coastline but it is expected to gradually meander northeastward
along the coast and eventually off the Tidewater VA area by
Thursday. The question will be just how far inland the precipitation
from the storm moves. At this time models don`t have a ton of
precipitation over the forecast area with best chances along the I-
95 corridor with only slight chances across the west. Expect diurnal
heating to drive thunderstorm chances with the greatest chance each
afternoon. Only expecting plus or minus a half of an inch of
rainfall...again with heaviest amounts in the east. Hot and humid
with highs in the mid 80s and lows in the mid to upper 60s.


.LONG TERM /Thursday Through Saturday/...
As of 245 AM Sunday...

Focus will shift away from Bonnie on Thursday and will instead
concentrate on a frontal system stemming from a low pressure system
over the Great Lakes. With the moist tropical airmass still in
place...diurnal showers and thunderstorms on Thursday afternoon will
be probable as the front approaches. The front will lose forward
progress on Friday and stall out over the east coast as an upper low
and trough opens up an extended moisture plume from the Gulf of
Mexico that will keep conditions wet for several days. Expect best
chance for thunderstorms during the afternoon and early evening
hours each day. High temperatures in the mid 80s with lows
continuing to be in the mid to upper 60s.


.AVIATION /12Z Sunday through Thursday/...
As of 615 AM Sunday...

FAY has already dropped to IFR in rain, and elsewhere, the current
VFR conditions will slowly deteriorate to MVFR or IFR later this
morning, although some brief improvement back to VFR may occur this
afternoon. The center of Tropical Storm Bonnie, currently located
off the SE coast east of SAV (see for the latest),
is expected to push slowly to the NW before stalling out near the
central SC coast through much of today. A surge of Atlantic moisture
to the NE of Bonnie will bring a band of showers toward the NNW
through central NC this morning into early afternoon, followed by
patchier and more widely scattered showers and perhaps a storm or
two during the mid to late afternoon, with the best chance of storms
at RDU/FAY/RWI. Within this first band of steady showers, cigs and
vsbys should drop to MVFR with cigs potentially IFR at times. Once
this main band shifts northward by early afternoon, conditions
should vary between MVFR and VFR through early evening. MVFR to IFR
fog and stratus are apt to redevelop after sunset, especially at
INT/GSO/RDU, with scattered showers persisting areawide.

Looking beyond 12z Mon: Unsettled weather will linger with periods
of sub-VFR conditions expected through Mon, including a good chance
of showers and storms Mon afternoon, especially at RDU/RWI/FAY. IFR
fog/stratus is likely to redevelop for Mon night / Tue morning.
Numerous sub-VFR showers and storms expected Tue afternoon at
RDU/RWI/FAY, with less coverage and mostly VFR conditions at
INT/GSO. Chances for sub-VFR showers diminish by Wed/Thu as the TS
Bonnie circulation and associated upper level disturbance finally
shifts NE away from the forecast area. -GIH





NEAR TERM...Hartfield
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