000 
fxus62 kmfl 201509 
afdmfl 


Area forecast discussion 
National Weather Service Miami Florida 
1109 am EDT sun may 20 2018 


Update... 
ample moisture continue to stream over South Florida. However, the 
area of heavy rain, which brought multiple Road closures across 
Broward County, has moved off to the north. There area areas of 
light to moderate rain still making their way into the area, and 
additional accumulations of 1 to 2 inches, with localized heavier 
amounts are still possible. Given Palm Beach saw most of the 
higher accumulations occur west of the Metro area, and Miami-Dade 
was missed by most of the significant accumulations, have allowed 
the Flood Watch to expire. However, have decided to extend the 
watch in Broward until 8 PM, as any high, or even moderate, 
accumulations may cause water to enter some structures across much 
of the Metro area. 


&& 


Previous discussion... /issued 847 am EDT sun may 20 2018/ 


Aviation... 
a trough extends across South Florida, and in conjunction with 
ample moisture, showers are forecast through the taf period. The 
showers may be heavy at times, bringing low cigs and vsby, 
sometimes below IFR criteria. The trough is forecast to take a 
westward shift today, possibly bringing some relief to the East 
Coast taf sites this afternoon, although at least -shra will 
remain possible. Some of the rain showers may also bring erratic winds to 
the area. 


Previous discussion... /issued 348 am EDT sun may 20 2018/ 


Discussion... 


Short term (today through tuesday) 
several bands of north/S oriented showers have moved ashore overnight 
from the Atlantic, with rainfall amounts averaging 0.75 to 1.5 
inches. These bands are associated with the convergence area on 
the periphery of the subtropical ridge, where the deepest tropical 
moisture has pooled. Expect this axis of moisture to remain over 
eastern parts of South Florida at least through this morning, 
bringing bouts of locally heavy rain. Thus, Flood Watch will 
persist through at least 11 am for Miami-Dade, Broward, and Palm 
Beach counties. See hydrology section for more information. 


Guidance suggests that the deep-layer ridge to our east will 
strengthen some and retrograde slightly west in the short term. 
This will gradually send somewhat drier air toward the region. 
However, at least through today, most of the area will remain in 
very high precipitable water airmass, with only inhibitor of widespread 
convection being abundant clouds which have thus far curbed 
instability and have played role in the lack of flooding rainfall 
in the past 24 hours. The corridor of deepest moisture is forecast 
to gradually shift to interior or West Coast of Florida today and 
tonight, then along the Gulf Coast Monday, before moving off the 
peninsula and bringing a relatively dry - as in only isolated to 
scattered showers/thunderstorms for Tuesday. At least some threat 
for locally heavy rainfall will remain Monday however. 
Temperatures today and Monday will be significantly impacted by 
rainfall, with maxima struggling to reach 80 degrees both days. 


Long term (tuesday night through saturday) 
it appears that any lull in precipitation Tuesday may be short- 
lived, with deep tropical moisture returning for the latter parts 
of the week. There is a great deal of uncertainty in the extended 
forecast as global models continue to diverge in solutions. European model (ecmwf) 
provides for a stronger/longer lasting subtropical ridge 
influence, leading to drier conditions through about Thursday, 
then greatly increasing rain chances as moisture-rich air pouring 
back into the region as a tropical disturbance moves toward the 
central Gulf. GFS, however, keeps moisture basically intact 
through the week with disturbance moving faster and in a more 
northeast direction, with perhaps drier air arriving in its wake 
at the end of the period. For now, will simply hold onto increased 
rain chances for the 2nd half of the week, but the potential for 
a return to heavy rainfall will have to be watched. More details 
on this potential can be found in the hydrology section below). 


Temperatures in the extended are based on the Assumption there 
will be many more breaks in the clouds than this weekend, allowing 
maxima to return to mid to upper 80s, and minima remaining 
generally in the 70s. 


Marine... 
winds will be slightly stronger today than Saturday, with 
southeast wind approaching 20 knots in Atlantic waters. Seas will 
also rise in the Atlantic to 3 to 5 feet. Conditions are forecast 
to be very close to advisory level, but for now will keep 
cautionary statement in place and continue to monitor for stronger 
wind. Similar conditions will likely prevail until about Tuesday. 
Widespread showers with some thunderstorms will persist through 
Monday, with the focus gradually shifting from the Atlantic into 
the Gulf (and continuing for lake okeechobee). The heavier 
activity could produce hazardous winds, locally higher waves, and 
dangerous lightning. 


Beach forecast... 
with southeast wind of 15 to 20 mph today, conditions are likely 
to be near the threshold for a high risk of rip currents on 
Atlantic beaches. For now will hold with moderate risk but will be 
closely monitoring for higher wind speeds and/or rip current 
reports. Similar conditions are likely into mid-week. 


Hydrology... 
grounds continue to saturate as drought conditions are 
ending/being alleviated across South Florida. Thus far, heaviest 
rainfall has been over the Naples area as well has Palm Beach and 
Broward counties. Today's highest totals (2 to 4 inches with 
isolated higher) are likely to be along the East Coast (where the 
Flood Watch is in effect). Watch may need to be extended if bands 
of showers dont propagate more westward with time. Additional 
heavy rain, averaging 1 to 2 inches, with locally higher amounts, 
are possible Monday, before a relative lull is expected into the 
middle of next week. Thereafter, will have to monitor for 
additional heavy rain/flood potential as deep tropical moisture is 
poised to return. Latest wpc 7-day forecast rainfall totals range 
from 3 to 7 inches, with greatest amounts across Southeast 
Florida. 
&& 


Preliminary point temps/pops... 
West Palm Beach 79 72 80 74 / 70 60 70 40 
Fort Lauderdale 80 74 82 74 / 90 60 70 40 
Miami 81 73 82 74 / 80 60 70 40 
Naples 81 71 83 72 / 90 40 60 40 


&& 


Mfl watches/warnings/advisories... 
Florida...Flood Watch until 8 PM EDT this evening for flz071-072-172. 


Am...none. 
GM...none. 
&& 






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