Debris Flow in Puerto Rico, June 28, 2020

Area Forecast Discussion...UPDATED
National Weather Service San Juan PR
1034 AM AST Sun Jun 28 2020

.UPDATE...Little change from yesterday. Temperatures will be
similar and dew points are running only about a degree lower. the
28/12Z sounding revealed less capping in the lower levels near 7
kft and better moisture up to 16 kft. CAPE values were higher
today, but the Lifted Index was slightly warmer. With the change
in wind, models are expecting better chances of precipitation over
southwest Puerto Rico and have added a slight chance of the
thunderstorm for more favorable conditions there, but rain chances
have not been changed elsewhere and Saharan dust persists that
will also limit convection elsewhere.

&&

.AVIATION...Saharan dust will limit visibilities to 7 miles in a
few select locations. SHRA are expected to dvlp in wrn and swrn PR
aft 28/17Z with a slgt chc of TSRA. Parts of the Cordillera
Central mtn range may be obscured til 29/23Z. Sfc winds 5-15 kt
with gusts psbl to 25 kt. Max winds WNW 50-65 kt btwn FL 380-480
but subsiding thru the day.

&&

.MARINE...Winds and seas will subside during the next 24 hours to
less than 6 feet and less than 18 knots. Small craft advisories
are not expected for the next 7 days. No change to expected rip
currents.

&&

.PREV DISCUSSION... /issued 655 AM AST Sun Jun 28 2020/

SYNOPSIS...Saharan dust will remain over the local area today and
therefore hazy skies are expected. Surface high pressure will
cause east to east northeast winds today, becoming mainly
easterly by Monday. An upper trough will cause instability and
thunderstorm activity through the first half of the workweek and a
weak tropical wave could approach the local islands by Thursday.

SHORT TERM...Today through Tuesday...

The presence of Saharan dust over the region will maintain
relatively tranquil weather today. However, there is some low
level moisture that could combine with the local effects,
resulting in shower activity in the afternoon across central to
southwestern PR due to an ENE wind flow. For Monday, the pattern
changes, an upper-level trough and induced surface perturbation
will approach the northeastern Caribbean. These features will
enhance upward motion and will increase the shower and
thunderstorm activity. Therefore, starting on Monday, isolated to
scattered showers are expected mostly over eastern sections of
Puerto Rico and the U.S. Virgin Islands in the morning. Then,
afternoon convection with moderate to heavy showers and isolated
thunderstorms are expected over the interior and western sections
of Puerto Rico in the afternoon. Also, showers will not be ruled
out across the San Juan Metro area. Urban and small stream
flooding is expected with the heaviest showers. This instability
due to the upper trough, is expected for the first few days of the
workweek, therefore a similar pattern in expected on Tuesday. In
term of temperatures, warmer than normal temperatures are expected
aross the coastal sections and urban areas with heat index values
that could be in the 100 to 105 degree range.

LONG TERM...Wednesday through Monday...

A slot of dry air is expected on Wednesday, ahead of a tropical
wave that could reach the local islands on Thursday. That said,
there may still be the influence of the upper trough, which will
help develop showers and thunderstorms across central to NW-PR on
Wednesday afternoon. The weak tropical wave that could reach the
area on Thursday may cause a significant enough increase in
moisture to cause showers and a few thunderstorms across a more
generalized area, with the latest GFS guidance favoring
development across the north half of PR. This pattern however is
trending differently than what the model was suggesting
yesterday, so not too much confidence is put in the long range
forecast. For the next weekend, patches of moisture will be moving
through, but by then, the upper low may not be positioned in a
location to provide good dynamics for generalized convection over
the local islands, so locally induced convection would be favored
starting on Friday and Saturday. However, some deeper moisture
could cause an increase in shower activity again on Sunday and
Monday.

AVIATION...Some haze is expected to continue today with visibilities
staying P6SM across all TAF sites. VFR conditions are expected
across the local TAF sites, but SHRA is possible at TJPS after
28/18Z. Winds out of the E-ENE between 10 and 15 kt with sea
breeze variations and occasional gusts.

MARINE...Winds of 10 to 15 knots are expected today with choppy
seas up to 6 feet. However, from this afternoon onward, most of
the local waters are expected to have wave heights up to 5 feet as
seas gradually subside. There is a moderate risk of rip currents
today across many of the local beaches, especially across northern
and southeastern Puerto Rico, Vieques and Culebra, west and south
Saint Thomas, south Saint John, as well as north, eastern and
southeastern Saint Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  90  79  88  77 /  30  40  40  50
STT  91  79  89  77 /  20  40  40  60

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

SHORT TERM...WS
LONG TERM....ICP
PUBLIC DESK...ICP

Perspectivas sobre Condiciones Peligrosas del Tiempo
Servicio Nacional de Meteorologia San Juan PR
1015 AM AST domingo 28 de junio de 2020

AMZ710>745-PRZ001>013-291415-
San Juan y Vecindad-Noreste-Sureste-
Este Interior-Norte Central-Interior Central-Ponce y Vecindad-
Noroeste-Oeste Interior-Mayaguez y Vecindad-Suroeste-Culebra-Vieques-
Aguas cercanas y mar afuera del Atlantico y Caribe-
1015 AM AST domingo 28 de junio de 2020

Esta perspectiva sobre las condiciones peligrosas del tiempo es para
Puerto Rico y las aguas costeras del Atlantico.

.Dia Uno...Hoy y esta noche

.Tronadas...Existe una probabilidad leve de tronadas con lluvia
fuerte y vientos en rafaga breves esta tarde a traves de sectores
del suroeste de Puerto Rico.

.Inundaciones... Se espera acumulacion de agua en las carreteras y
en areas de pobre drenaje.

.Viento...Vientos sostenidos en exceso de 20 mph (17 nudos se
esperan a traves de las aguas locales y algunas areas costeras.

.Oleaje...Oleaje de hasta 6 pies a traves de las
aguas mar afuera del Atlantico y del Caribe y los pasajes locales.

.Corrientes Marinas...Existe un riesgo moderado de corrientes
marinas para la mayoria de las playas locales.

.Calor... Temperaturas por encima de lo normal y humedad causaran
indices de calor de entre 100 a 105 grados a traves de las areas
bajas, en areas aisladas podrian ser mayor por solo un periodo corto
de tiempo.

.Dias dos hasta el siete...lunes a sabado

Una Vaguada a los niveles altos aumentara el potencial de actividad
de aguaceros y tronadas para la mayoria de la proxia semana. Se
esperan inundaciones urbanas y de pequenos riachuelso con las
lluvias mas fuertes. Se espera que prevalezacan condiciones
maritimas tranquilas para el resto de la semana con oleaje de hasta
6 pies. Indices de calor entre 100 y 105 grados pueden observarse
durante los proximos dias.

.Comunicado sobre informacion reportada por observadores...

No se anticipa activacion de observadores, sin embargo, se
recomienda a los observadores individuales que reporten
inundaciones, vientos, olas y corrientes marinas al Servicio
Nacional de Meteorologia en San Juan mientras siguen las
indicaciones de las autoridades locales y estatales.

AMZ715-725-VIZ001-002-291415-
San Tomas, San John y Islas Adyacentes-Santa Cruz-
Aguas cercanas del Atlantico y aguas costeras adyacentes del Caribe-
1015 AM AST domingo 28 de junio de 2020

Esta perspectiva sobre las condiciones peligrosas del tiempo es para
Islas Virgenes Estadounidenses y las aguas costeras adyacentes.

.Dia Uno...Hoy y esta noche

.Viento...Vientos sostenidos en exceso de 20 mph (17 nudos se
esperan a traves de las aguas locales y algunas areas costeras.

.Oleaje...Oleaje de hasta 6 pies a traves de las
aguas mar afuera del Atlantico y del Caribe y los pasajes locales.

.Corrientes Marinas...Existe un riesgo moderado de corrientes
marinas para la mayoria de las playas locales.

.Calor... Temperaturas por encima de lo normal y humedad causaran
indices de calor de entre 100 a 105 grados a traves de las areas
bajas, en areas aisladas podrian ser mayor por solo un periodo corto
de tiempo.

.Dias dos hasta el siete...lunes a sabado

Una Vaguada a los niveles altos aumentara el potencial de actividad
de aguaceros y tronadas para la mayoria de la proxia semana. Se
esperan inundaciones urbanas y de pequenos riachuelso con las
lluvias mas fuertes. Se espera que prevalezacan condiciones
maritimas tranquilas para el resto de la semana con oleaje de hasta
6 pies. Indices de calor entre 100 y 105 grados pueden observarse
durante los proximos dias.

.Comunicado sobre informacion reportada por observadores...

No se anticipa activacion de observadores, sin embargo, se
recomienda a los observadores individuales que reporten vientos,
oleaje y corrientes marinas al Servicio Nacional de Meteorologia en
San Juan mientras siguen las indicaciones de las autoridades locales
y estatales.