Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/28/21
Area Forecast Discussion
National Weather Service Key West FL
1156 PM EDT Fri Aug 27 2021
.DISCUSSION...
Currently - Hurricane Ida has recently emerged off the northwest
Cuban coast and into the Gulf of Mexico. Ida is being steered
around the lower tropospheric ridge which extends across the
southern states and broadens across the east coast, then east
southeastward north of the Bahamas. Latest aircraft recon
indicated a minimum surface pressure of 993 mb and SFMR winds of
35 to 50 knots across our western most Florida Straits zones.
SFMR also measured winds of 30 to 35 knots over the waters just
southwest of the Dry Tortugas. After several rounds of showers and
a few thunderstorms earlier this evening, the resulting broad and
largely stratiform running from around the Dry Tortugas, across
the Lower Keys to the outer Florida Straits off of the Middle Keys
has steadily congealed into showers with a few embedded
thunderstorms. Some of this activity has been strong.
Short Term Update - Ida will continue to work it way northwestward
through the southeastern Gulf of Mexico tonight, and into the
Central Gulf of Mexico on Saturday. Through this, Ida will
steadily put more miles between itself and the Florida Keys. Winds
will, overall trend downward. With that said, initially, any
decrease will be slow to occur and significant wind of 30 to 40
mph and locally higher gusts are likely within passing fast moving
convective features. Have raised pops in the Lower Keys to
categorical and kept a high chance in the Upper Keys. Only minor
adjustments made an evening zone update.
&&
.MARINE...
Ida continues to move northwestward through the southeastern Gulf
of Mexico and around a Ridge extending from north of the Bahamas
to the eastern United States. A Tropical Storm Warning remains in
effect for the Florida Straits adjacent to the Dry Tortugas, and
an advisory remains in effect for remaining waters west of Craig
Key. Recent aircraft recon have indicated winds of 35 to 50 knots
on waters south of the Dry Tortugas. Once Ida begins to pull
further away from all Keys waters, winds will start trend
downwards and seas will gradually improve. The best timing for
this will be from late in the overnight and through Saturday.
Meanwhile, fast moving showers and embedded thunderstorms present
along a band from the area around the Dry Tortugas to the outer
Florida Straits off of the Middle Keys will be capable of
producing wind gusts well in excess of 35 knots.
&&
.AVIATION...
While prevailing VFR conditions will persist at island terminals
overnight, rapidly moving showers and possibly a thunderstorm will
result in brief periods of sub VFR conditions. The timing and
location of these showers is difficult to predict at this time.
With that said, vicinity SHRA and sub VFR TEMPOs have been
included. Surface winds will be out of the east southeast at 15 to
25 knots with the stronger winds at EYW due to proximity to
passing Ida. Fast moving showers will likely produce wind gusts in
excess of 30 to 35 knots. The strongest winds at both terminals
will be during the onset of showers or squalls.
&&
.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...Small Craft Advisory for GMZ032>035-043-044-053-054-073-074.
Tropical Storm Warning for GMZ055-075.
&&
$$
Public/Marine/Fire...11
Aviation/Nowcasts....Devanas
Data Acquisition.....DR
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Area Forecast Discussion
National Weather Service Phoenix AZ
420 PM MST Fri Aug 27 2021
.UPDATE...
Updated Aviation
&&
.SYNOPSIS...
Storm chances will gradually increase from east to west over the
next few days, however still primarily affecting higher terrain of
eastern Arizona. A much more unsettled weather pattern is expected
for the first half of next week as tropical moisture surges into the
region Monday and Tuesday. This should bring good chances for
rainfall through the middle of next week, likely focused across
south central Arizona, while also bringing much cooler temperatures
as well.
&&
.DISCUSSION...
Objective analysis this afternoon shows mid-level anticyclonic
circulation centered directly over south-central AZ with 500 mb
heights around 590-592 dm. This is resulting in another very hot day
across the lower deserts with temperatures in the 110-115 degree
range. As of 3:30 PM, Phoenix Sky Harbor has been up to 112F, only 1
degree shy of tying the daily record of 113F last set in 2020. An
Excessive Heat Warning continues through this evening for south-
central AZ and has been extended through Sunday for southwest AZ and
southeast CA. The latest NBM forecast has high temperatures dipping
a few degrees into the weekend, with highs around 110-113 in
southwest AZ and southeast CA and highs just shy of 110 in south-
central AZ. While the warning drops off for south-central AZ, people
should still be cognizant of the hot, above normal, temperatures and
continue to take precautions, especially with it being a weekend.
Shower and storm chances across the CWA show a gradual trend upwards
through the next several days, with NBM PoPs increasing and
spreading slightly further west each day. Today, with the
anticyclone directly overhead, shear is nonexistent. PWAT values are
also quite low, with recent aircraft soundings showing values around
1", but with marginal MLCAPE around 500-1000 J/kg and minimal
capping, isolated to scattered showers and storms have been able to
develop across portions of eastern and southeastern AZ. With the
very weak shear and low PWAT, many storms will likely rain
themselves out after precip-loading overwhelms the updraft. Still, a
quick burst of heavy rain could lead to very localized flash
flooding impacts, especially with any storms that anchor over
terrain features. DCAPE is high with the drier boundary layer
conditions, so the primary storm threat through the afternoon will
be damaging winds along with the potential for blowing dust,
especially in dust prone areas like Pinal county. While convection
should diminish after sunset, a few hi-res models are suggesting mid-
level gravity waves from this afternoon`s storms could generate some
westward-moving elevated convection into the overnight hours, mostly
across southern AZ.
For this weekend, the aforementioned anticyclone is expected to
drift toward northern AZ, resulting more of a northeasterly mid-
level steering flow and a better setup for Rim to Valley storms.
Storms in the Valley the next couple afternoons may still be
dependent on how stable conditions are and perhaps conditional on a
strong outflow boundary/boundaries and/or boundary collisions. NBM
PoPs in the Phoenix metro area are only around 10-20%. HREF is
supporting greater coverage of convection along the Rim on Saturday
as well as down in the Tabletop area of southwest Maricopa county.
Convection in the Kofas and parts of eastern La Paz county will also
likely be more common this weekend. With the lower moisture levels
and dry boundary layer, flash flooding at lower elevations will be
less of a threat this weekend than damaging winds and dust, but
shouldn`t be disregarded. The HREF probability of wind speeds
greater than 35 mph across the lower deserts Saturday
afternoon/evening is up to 40-60%, with a 10% chance for greater
than 58 mph through the dust prone areas of Pinal county and I-8 in
southwest Maricopa county.
&&
.PREVIOUS DISCUSSION...
Next week continues to look more and more intriguing as we are very
likely to see tropical moisture surge northward into our region
starting Monday out ahead of Tropical Storm Nora. The latest NHC
forecast has Nora reaching the southern tip of Baja sometime Sunday
night/early Monday and then making some progress northward into the
Baja/Gulf of California area. At the same time an upper level trough
will be taking shape just west of Baja, likely strengthening Sunday
into Monday as it drifts to the north before affecting our region
into the middle part of next week likely interacting with the
tropical moisture from Nora. Although some uncertainty remains with
the evolution and timing of both the upper level trough and Nora,
model ensembles generally agree some part of our region is likely to
see significant rainfall.
For now, it seems there is decent model consensus of the best
chances for widespread rainfall occurring across southern into
central Arizona late Tuesday into Wednesday. However, we can`t rule
out decent rainfall across eastern Arizona into possibly the south-
central Arizona deserts as early as late Monday, as shown by a good
number of GEFS members. Although timing is still fairly uncertain,
there is increasing forecast confidence in a threat for heavy
rainfall and possible flooding at some point between late Monday and
early Thursday of next week. NBM forecast temperatures also show a
big cool down into the middle part of next week with highs possibly
in the lower 90s in the Phoenix area to the upper 90s across
southeast California. Would not be surprised if these forecast highs
drop further, especially if we see 2" PWATs back into our area which
is currently shown for next Tuesday and Wednesday.
&&
.AVIATION...Updated at 2320Z
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
While thunderstorms this evening should remain well outside visual
ranges, distant outflows could result in an earlier, and somewhat
enhanced easterly switch. Confidence is moderate that very little
gustiness will occur with the highest probability of winds in excess
of 15-20kt at KIWA. Only FEW-SCT mid/high clouds will be common.
Better chances of thunderstorm impacts are likely late Saturday
afternoon and evening with models suggesting an organized outflow
boundary creating gusty NE winds sweeping through all terminals.
Southeast California/Southwest Arizona including KIPL and KBLH:
No weather impacts should exist through Saturday afternoon under
mostly clear skies. Winds will generally favor southeast headings at
KIPL aside from downsloping westerlies during the evening and
overnight. Directions at KBLH will mirror the past couple days with
afternoon/evening southerly, and overnight/morning drainage
northerly. Wind speeds will remain at or below 12 knots aside from
the potential for a brief 15-20 knot gust this evening.
&&
.FIRE WEATHER...
Sunday through Thursday:
Increasing moisture and rain chances will be seen through early
next week with temperatures eventually cooling to below normal by
Tuesday. Shower and thunderstorm chances on Sunday will mostly be
limited to the high terrain before spreading into the lower deserts
starting Monday. Widespread wetting rains then look likely Tuesday
into Wednesday as tropical moisture surges into the region. Minimum
RH values will increase from 15-20% on Sunday to 30-40% by Tuesday,
staying elevated through the rest of the period. Maximum RH values
will increase from 40-50% to 60-80% by midweek. Winds should be
relatively light with an afternoon upslope component and overnight
drainage common. Some enhanced afternoon and evening gusts will be
possible at times in western districts.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST this evening for AZZ534-
537>544-546-548>556-559>562.
Excessive Heat Warning until 8 PM MST Sunday for AZZ530>533-535-
536.
CA...Excessive Heat Warning until 8 PM PDT Sunday for CAZ560>570.
&&
$$
DISCUSSION...Benedict
PREVIOUS DISCUSSION...Kuhlman
AVIATION...18
FIRE WEATHER...Kuhlman