Area forecast discussion
National Weather Service Miami Florida
1013 am EDT sun may 19 2013
Update...
high pressure ridge continues in control across the local area.
Upper level short wave along east central Florida coast and
associated area of convection has continued to weaken this
morning. 12z upper air analysis shows easterly flow this morning
has deepened with convective indices a bit less impressive than
yesterday as middle levels are warmer. Mean layer storm motion is generally
from the NE around 3 knots, basically meaning nearly no motion
with sea breeze interactions and outflow boundaries this afternoon
dictating where storms will end up developing and going. Ensemble
of high resolution models including hrrr, local WRF configs, and
nationals all hint at development just around or west of the East
Coast metropolitan areas from around noon into the early to middle afternoon
with activity focusing across the interior and West Coast as we
head into the evening hours. It is Worth mentioning a couple of the
members do hint at activity developing right over the East Coast
metropolitan areas which despite deeper easterly flow is still possible
given the slow storm motion. Given thermodynamic indices there is
still a chance of frequent lightning with some of the storm, gusty
winds, and small hail but it is a remote chance at best, and less
than yesterday. Locally heavy rainfall is another concern given
slow motion of the storms but again best chance will be over the
interior. Grids and forecasts updated accordingly.
&&
Previous discussion... /issued 849 am EDT sun may 19 2013/
Aviation...
a small area of MVFR ceilings continue to linger near the East Coast
terminals this morning. Easterly flow will persist across the area
with high pressure situated across the western Atlantic. Short
range models depict a Gulf Breeze developing around 17z which
should provide enough of a focus for scattered shower and
thunderstorm development. Believe most of the activity should
remain confined across the western interior but could build back
west toward kapf. Kept out any thunder mention for now and covered
with vcsh. Kept East Coast terminals dry at this time.
Previous discussion... /issued 255 am EDT sun may 19 2013/
Short term (today-tuesday)...
recently animated water vapor loop was characterized with an upper
ridge extending north over the MS valley gradually building eastward
with northwest flow streaming over the state out ahead of it. A few
weak impulses embedded within this northwest flow will continue to
influence the local weather through the short-term period. The
morning surface analysis depicted the subtropical ridge axis
extending west across central Florida with light southeast winds
over South Florida.
The latest numerical guidance has initialized well with these
synoptic features and generally indicates increasing deep layer
moisture along with an upper low closing off overhead by Tuesday.
Model soundings reflect this and generally indicate slightly cooler
500 mb temperatures and decent middle-level lapse rates each day. The middle-level
cap that was evident yesterday from 650-700mb is forecast to
diminish today. These factors combined with light southeast
low-level flow...increasing moisture and daytime heating will only
enhance the diurnally induced convection each day through the
afternoon and early evening periods. Sea breeze and mesoscale
boundaries will serve as the focus for shower/thunderstorm initiation each
day...especially across the interior where the Gulf and Atlantic
breezes converge. Although the severe thunderstorm threat remains
low...a few strong storms will certainly remain possible with the
main impacts being hail and damaging straight-line winds (40-55
mph). The best chance for East Coast/metropolitan showers will be through
the late night and early morning hours as showers develop over the
Atlantic and spread ashore. Model soundings do indicate more of a
northerly upper flow today...so cirrus blow-off shouldn't impact
the East Coast temperatures as much as yesterday afternoon.
Temperatures will remain around or slightly above normal through
the period.
Long term (wednesday-sunday)...
the GFS/GFS ensemble mean and European model (ecmwf) generally remain in good
agreement through the extended period and indicate a persistent
upper trough/low continuing to influence the local area through the
middle-week period. A surge of deep layer moisture later in the week
associated with a weak surface trough embedded in the easterly flow
combined with the upper low could lead to more widespread rainfall
activity Wednesday through Thursday. The GFS and European model (ecmwf) both indicate
this weak surface reflection further developing as a surface low
lifting north over the state on Thursday. Despite the consistency
from run to run over the past 24 hours...we will remain steady with
the rainfall chances since this is still beyond the 72 hour time
frame. Any shift to the east as this surface feature lifts north
could keep the bulk of the rainfall east of the area. Drier air will
overspread the area as this feature lifts north Friday through the
weekend.
Aviation...
VFR conditions to prevail at all sites through the period. Easterly
flow will persist across the area with high pressure situated across
the western Atlantic. Short range models depict a Gulf Breeze
developing around 17z which should provide enough of a focus for
scattered shower and thunderstorm development. Believe most of the
activity should remain confined across the western interior but
could build back west toward kapf. Kept out any thunder mention for
now and covered with vcsh. Kept East Coast terminals dry at this time.
Marine...
light to moderate east and southeast winds will continue through
much of the forecast period as high pressure remains in control
northeast of the marine area. Isolated overnight and early morning
showers will remain possible each day across the Atlantic waters. A
weak surface trough will lift north over the state through the
middle-week period and will lead to increasing rainfall chances and
possibly a period or two with near advisory level winds and seas
over the Atlantic waters.
Fire weather...
southeast low-level winds along with increasing moisture and rain
chances will be expected through the week. Most of the showers
and storms that develop will be focused along the East Coast through
the early morning hours and across the interior locations through
the afternoon/evening periods. More widespread rainfall activity
will be possible through the middle-week time frame.
&&
Preliminary point temps/pops...
West Palm Beach 86 74 84 72 / 20 20 20 20
Fort Lauderdale 84 75 85 74 / 20 20 20 20
Miami 85 75 85 74 / 20 20 20 20
Naples 89 71 88 70 / 30 30 30 30
&&
Mfl watches/warnings/advisories...
Florida...none.
Am...none.
GM...none.
&&
$$
Discussion/marine/fire...52/ps
aviation/radar...84/AK
