AXNT20 KNHC 211205
Tropical Weather Discussion
NWS National Hurricane Center Miami FL
805 AM EDT Mon May 21 2018
Tropical Weather Discussion for North America, Central America
Gulf of Mexico, Caribbean Sea, northern sections of South
America, and Atlantic Ocean to the African coast from the
Equator to 32N. The following information is based on satellite
imagery, weather observations, radar and meteorological analysis.
Based on 0600 UTC surface analysis and satellite imagery through
Upper level cyclonic wind flow spans the Gulf of Mexico. A trough
extends from the Florida Panhandle, beyond the Yucatan Channel,
into the NW Caribbean Sea. This weather pattern is drawing deep
tropical moisture northward, from the SW Caribbean Sea between
76W and 84W, and is supporting scattered to numerous moderate to
strong rainshowers, from the SW Caribbean Sea, across Cuba, to
Florida, and the Bahamas and the nearby Atlantic Ocean. This
activity is expected to continue through at least Tuesday, with
heavy rainfall and flooding.
A tropical wave is along 12N33W 07N34W 01N35W, moving W 10 to 15
knots. This wave is embedded in a sharp 700 mb trough. Although
deep moisture accompanies the wave, subsidence from aloft is
inhibiting convection except over the southern portion. Scattered
moderate convection is from 00N to 04N between 29W and 35W.
A tropical wave is just to the east of the Caribbean Sea, along
59W from 16N southward. This wave continues to appear as a 700 mb
trough and has a poleward surge in moisture associated with it.
Scattered showers and isolated thunderstorms are within 300 nm of
either side of the trough axis. This trough will enter the E
Caribbean by Tuesday and then will become ill defined.
The monsoon trough passes through coastal Africa near 11N15W to
05N20W. The ITCZ extends from 05N20W to 03N31W, then resumes west
of a tropical wave from 01N35W to 00N51W. Besides the convection
associated with the wave, isolated moderate convection is from 01N
to 07N between 11W and 28W.
GULF OF MEXICO...
An upper-level trough prevails across the eastern Gulf, with an
axis along 85W. Diffluent flow aloft east of the trough is
bringing tropical moisture over the far east Gulf and western
Atlantic waters affecting the Florida Peninsula and Florida
Straits/Keys. Please refer to the Special Features section above for
more details. A surface trough is embedded underneath the upper
trough, and as of 0300 UTC has an axis that extends from 30N84W
to near 23N85W. A weak ridge axis extends across the remainder of
the basin along 30N producing mainly gentle to moderate winds. A
weakening line of thunderstorms has emerged within 120 nm E of the
SE Texas coast as of 0300 UTC and will likely affect those waters
A surface ridge will remain in the northern Gulf Coast through
Thursday night. The current eastern Gulf of Mexico surface trough
will drift westward through at least Wednesday. It is possible
that a low pressure center may develop along the trough, in the
the NW Caribbean Sea, toward the end of the work-week.
An upper-level trough extends over the eastern Gulf of Mexico and
western Caribbean. A surface trough is over the western Caribbean
and as of 0300 UTC had an axis extending from 21N85W to 11N83W.
The combination of upper- level diffluence on the eastern side of
the upper-level trough and convergence associated with the surface
trough is supporting scattered to numerous moderate convection
across the Caribbean waters between 78W and 84W. Broad high
pressure over the subtropical Atlantic continues to support
moderate to fresh tradewinds over most of the basin, except fresh
to strong winds over the central Caribbean. Wave heights of 8 to 9
ft persist over the central Caribbean as confirmed by both satellite
altimeters and current buoy data.
Atlantic Ocean high pressure will maintain fresh to
locally strong trades over the central Caribbean through Fri
night. Strong winds and seas to 9 ft will affect the NW coast of
Colombia. A western Caribbean Sea surface trough will drift
westward across Central America through at least Thursday. It is
possible that a low pressure center may develop along the trough,
and move across Nicaragua and Honduras, emerging into the Gulf of
Honduras by Thursday. The pressure gradient between the trough
and the Atlantic Ocean high pressure will result in fresh to
strong winds in the central Caribbean Sea, and in parts of the
western Caribbean Sea.
Diffluent flow aloft to the east of an upper-level trough
currently over the eastern Gulf of Mexico, combined with a surface
trough extending just offshore of northern Florida is supporting
scattered to numerous moderate convection across Florida, the
Bahamas, and Atlantic waters mainly west of 76W. To the east, high
pressure centered over the central Atlantic spans across the basin.
Surface observations and latest scatterometer data indicate
prevailing fresh to locally strong southeast winds over the
Bahamas as well as within a few hundred miles north of Hispaniola
and Cuba. A recent altimeter pass indicates wave heights of 8 to
9 ft over these waters as far N as 26N outside of the Bahamas.
Moderate to fresh tradewinds are occurring elsewhere across the
central and western Atlantic south of 27N. Gentle to moderate
winds cover the central Atlantic north of 27N. Moderate to
occasionally fresh northeast winds are occurring over the eastern
The chances for heavy rainfall in Florida, across the Bahamas,
and in the western Atlantic Ocean will continue.
An east-to-west oriented ridge will be along 30N through the
middle of the week. The ridge will support fresh to locally
strong E to SE winds mainly S of 26N, including the Old Bahama
Channel, and the approaches to the Windward Passage through Tue
night. Fresh to occasionally strong winds will prevail N of
Hispaniola, mainly at night. A broad area of low pressure may
develop over the NW Caribbean Sea and move northward across the
eastern Gulf of Mexico. This will cause strong SE to S winds to
develop over the waters W of 75W late Fri into Sat.
For additional information please visit