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Area Forecast Discussion (AFD)

Issued by Key West, FL (KEY)

                            
101 
FXUS62 KKEY 210855
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
455 AM EDT Sat Jul 21 2018

.DISCUSSION...
A mean layer ridge complex anchored over the southern Plains
reaches southeast into the central Gulf of Mexico. The western
extent of the low level subtropical ridge persists across the
Florida Keys, maintaining weak steering flow and light surface
breezes. Temperatures are in the mid 80s with dewpoints in the mid
70s. The KBYX radar is nearly echo free. Last evening's sounding
sampled near record low PW and significant low level inhibition. A
developing low pressure system moving northeast near the Carolina
Coasts has weakened the mean layer ridging over the eastern Gulf 
of Mexico and North Florida. 

.SHORT TERM (Today through Monday)...
Water vapor imagery highlights a deep trough complex over the
Great Lakes. This system will slowly carve out lower heights from
the southeastern United States to the Gulf of Mexico over the 
next few days. Low level ridging over the Keys will remain 
resilient today and tonight, then give way Sunday and Sunday 
night. Deep and weakly cyclonic flow will develop over the Keys on
Monday. The vertical profile appears to moisten considerably as 
the outer fringes of the trough complex instigates moisture 
advection. Rain chances will increase Sunday and Sunday night, 
culminating in 40% chances on Monday. Through the short term, lows
will range from 80 to 85 and highs will climb well into the 90s. 
A breeze will finally develop by Monday afternoon, ending the long
streak of winds near 5 knots or less. 

&&

.LONG TERM (Monday night through Friday)...
The low level ridge will begin to push back against the trough
complex in the Gulf Monday and Monday night. By Tuesday,
southwesterly steering will open up chances for afternoon Cuban 
convection to make the long trek through the Straits of Florida,
possibly impacting the island chain each evening. Vertical
profiles indicate the invasion of occasional dry layers Tuesday 
through Thursday. Thus, rain chances have been tempered to 40% 
through this stretch, in line with the MOS consensus and just 
above climatology. The subtropical ridge will rebuild to the north
of the Keys in earnest Thursday night and Friday. Undulations in 
the east-southeasterlies likely will necessitate increased rain 
chances into next weekend. 

&&

.MARINE...
A weak pressure pattern will prevail today and tonight. Despite
the weak pattern, the heating of South Florida will result in
enhanced breezes adjacent to the peninsula late each afternoon. A
broad and weak area of low pressure will develop over the 
southeastern United States Sunday and Sunday night, then slide 
southwest into the northeastern Gulf of Mexico Monday and Monday 
night. This area of low pressure will recede to the north 
Wednesday and Wednesday night. 

&&

.AVIATION...
Until 00z/22nd, VFR conditions will prevail at the Key West and 
Marathon terminals. Mainly south winds near 5 knots will turn west
at 5 to 10 knots this afternoon. 

&&

.CLIMATE...
In 1946, the daily record low temperature of 72 degrees was last 
recorded in Key West. Temperature records date back to 1872.

&&

.PRELIMINARY POINT TEMPS/POPS...
Key West  92  83  93  83 / 10 10 20 30 
Marathon  94  83  95  83 / 10 10 20 30 

&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&

$$

Public/Marine/Fire...CLR
Aviation/Nowcasts....APA
Data Collection......DR

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