National Weather Service United States Department of Commerce

TC Graphics (Track and Error Cone, Wind Speed Probabilities, Time of Arrival)

Tropical Cyclone (TC) graphics available following updated bulletins issued by the Joint Typhoon Warning Center (JTWC) for cyclones within our AOR (Area of Responsibility) - extends out 300 nautical miles from Tutuila, American Samoa. Read More >

The National Weather Service issued forecasts for sky condition, temperature, wind and precipitation on a routine basis. The terminology used in these forecasts is quite variable. Listed below are descriptors of regularly used weather terms and their meanings to help give a better understanding of each forecast.


Sky Condition


The sky condition describes the predominant/average sky cover based on percent of the sky covered by opaque (not transparent) clouds. If a high probability of precipitation (60% or greater) is expected, then the sky condition may be omitted since it is inferred from the precipitation forecast.

Sky Condition Opaque Cloud Coverage
Clear/Sunny 1/8 or less
Mostly Clear/Mostly Sunny 1/8 to 3/8
Partly Cloudy/Partly Sunny 3/8 to 5/8
Mostly Cloudy 5/8 to 7/8
Cloudy 7/8 to 8/8




The wind describes the prevailing direction from which the wind is blowing with speeds in miles per hour. The wind forecast is included in the first three periods of the zone forecast.

Sustained Wind Speed Descriptive Term
0-5 mph Light/ light and variable wind
5-10 mph/ 10-15 mph/ 10-20 mph None
15-25 mph Breezy 
20-30 mph Windy
30-40 mph Very Windy
40 mph or greater Strong, dangerous, high, damaging (High Wind Warning Criteria)


Precipitation Probability


The probability of precipitation (POP), is defined as the likelihood of occurrence (expressed as a percent) of a measurable amount of liquid precipitation (or the water equivalent of frozen precipitation) during a specified period of time at any given point in the forecast area. Measurable precipitation is equal to or greater than 0.01 inches. Unless specified otherwise, the time period is normally 12 hours. NWS forecasts use such categorical terms as occasional, intermittent, or periods of to describe a precipitation event that has a high probability of occurrence (80%+), but is expected to be of an "on and off" nature.

POP Percent Expression of Uncertainty Equivalent Areal Qualifier
10 percent (none used) Isolated/ Few
20 percent Slight Chance Widely Scattered
30, 40, & 50 percent Chance Scattered
60 & 70 percent Likely Numerous (or none used)
80, 90, & 100 percent (None used) Occasional, periods of, or none used


Time Periods


Forecast Time Period NWS Definition (LST)
Today 6am-6pm
This Morning 6am-noon
This Afternoon Noon-6pm
This Evening 6pm-midnight
Overnight Midnight-6am
Tonight 6pm-6am