Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KRAH 290058
Area Forecast Discussion
National Weather Service Raleigh NC
845 PM EDT Sat May 28 2016
.SYNOPSIS...Tropical storm Bonnie off the Southeast coast will
track northwest to the South Carolina coast tonight, stall along the
South Carolina coast on Sunday, then track slowly northeast along or
just offshore the North Carolina coast through mid-week.
.NEAR TERM /Through Tonight/...
As of 841 PM Saturday...
The latest information from the NHC indicated that TS Bonnie had
stalled in the last few hours. It is expected to resume the NW
movement but less than 10kt this evening as it tracks toward the
southern SC coast. There continued to be an impressive plume of deep
moisture advecting NW to the east of the center of circulation of
Bonnie. At the surface, a surface trough or wind shift line had
advanced westward into the Piedmont from the Coastal Plain at mid-
evening. Dew points jump into the mid to upper 60s from the upper
50s as the trough moves passes and winds become more easterly off
the Atlantic. An initial rain band was rotating NW toward the SE NC
coastal region this evening. It appears that it will be late evening
before some of this band moves into our southern Coastal Plain. We
will ramp up POP in the SE to account for this activity and
additional rain later on. Conversely, we will cut POP back for the
NW-N zones to a slight chance through 06Z, then as the rain/showers
develop and spread NW-W increase POP between 06Z-12Z throughout the
region. It appears a surface trough will set up over the region
later tonight into Sunday. It should be along this convergence axis
that rain/showers become widespread later tonight and Sunday. With
dew points rising and skies becoming cloudy, expect lows 65-70 SE
and lower to mid 60s NW.
.SHORT TERM /Sunday through Sunday night/...
As of 200 PM Saturday...
TD#2 is expected to become a low-end tropical storm prior to
landfall (or closest approach to the SC coast) around 12Z Sunday
morning. The precise evolution of this system (the track in
particular) will heavily influence the location/amount of rain that
falls across central NC Sunday into Sunday night, as demonstrated by
the wide variety of solutions obtained from various convection
allowing models. As a result, the location(s) or area(s) that will
receive the heaviest rainfall remain difficult to pin-down at this
time. Based on the official NHC guidance, one would expect the axis
of heaviest rain to become oriented N-S or NNE-SSW in vicinity of
Highway 1 or I-95. Locally heavy rainfall amounts of 1-3" will be
possible in this area. High temps will depend primarily upon cloud
cover and precipitation, which should be pervasive over much of
central NC. As such, will indicate highs in the mid/upper 70s,
though lower 80s will be possible if/where there are breaks in cloud
cover. Expect lows in the mid/upper 60s (possibly near 70F) Sunday
night with a tropical airmass in place, southeasterly flow off
the Atlantic, lingering cloud cover, and showers.
Hazardous Weather: A localized potential for flash flooding will be
present Sun/Sun night, primarily in urban areas. Given the
anticipated location of TD#2 (expected to stall in southern SC
during the day Sun), the best low/mid-level shear (mini-supercell/
tropical tornado potential) is expected to remain south of central
NC, along and near the coast from Charleston SC north to Wilmington,
.LONG TERM /Monday Through Saturday/...
As of 310 pM Saturday...
Monday through Wednesday: The low associated with tropical
depression two will be captured in a weakness or trough in the upper-
level pattern over the southeast U.S. and a 590m ridge over the
western Atlantic. This will result in a very slow east to northeast
drift of the surface low as the ridge over the Atlantic weakens.
The best precipitation chances during the period should be focused
across central the eastern half of NC and in our forecast area across
the coastal Plain/Sandhills and the eastern Piedmont. This is given
the northward advection of deep layer moisture on the backside of
the offshore ridge and to the east of the trough axis combined with
some modest forcing for ascent east of the trough and low-level
convergence resulting from the tropical circulation and frictional
convergence in the coastal region.
The greatest rain chances during the period will likely be on Monday
east of U.S. route 1 where rain coverage and amounts will be
greatest. Rain chances decrease somewhat on Tuesday and Wednesday.
Rainfall amounts will be rather localized with slow moving bands and
clusters of showers/storms driving precipitation amounts. Average
amounts through the period will range around an inch to an inch and
half from I-95 east, a half inch to an inch between U.S. 1 and I-95
and a half inch or so west of U.S. 1. While these amounts
aren`tterribly impressive, we fully expect localized higher amounts
during the period. Highs during the period will generally range in
the lower 80s on Monday and the lower to mid 80s on Tuesday and
Wednesday with morning lows in the mid to upper 60s.
Thursday through Saturday: A slow moving trough pushes east across
the plains on Thursday and extends from the eastern Great Lakes to
the northern Gulf of Mexico on Friday and Saturday. The eastern
progression of the trough slows as heights rise off the Southeast
coast and the remnants of TD two eventually dissipate off the
Northeast coast. The developing southwesterly flow ahead of the
approaching upper trough leads to another period of moisture
transport with increasing instability. After a modest
decrease precipitation chances on Thursday in between systems and
with a minimum which should result in a period of unsettled weather
for Friday into Saturday with showers and thunderstorms. highs will
mainly range in the lower to mid 80s with lows in the 60s. -blaes
.AVIATION /00Z Sunday through Thursday/...
As of 8 PM Saturday...
24-Hr TAF Period: A plume of tropical moisture will advect into the
area overnight and into the day on Sunday as TS Bonnie moves onshore
between Charleston and Beaufort, SC. Ceilings are expected to lower
to MVFR/IFR from SE to NW between 06z-12z, with increasing chances
for showers and associated sub-VFR visibilities expected at all
terminals by mid/late morning. Sub-VFR ceilings and visibilities
will persist through the afternoon and evening with numerous heavy
rain producing showers across the area, along with a threat for
isolated thunderstorms mainly across the eastern terminals.
Looking Ahead: Unsettled weather with continue Sunday night through
Monday as TS Bonnie and associated tropical moisture plume linger
across the area. Significant uncertainty persists whether or not
remnants of Bonnie stalls along the Carolina coast through mid to
late week. At this time, a chance for diurnally driven convection
and morning stratus are expected to be the primary aviation hazards.