Station 41002 (LLNR 830) - SOUTH HATTERAS - 225 NM South of Cape Hatteras Image indicating link to RSS feed of recent meteorological observations for station 41002


Conditions at 41002 as of
(8:40 am EDT)
1240 GMT on 05/24/2024:
     

Click on the graph icon in the table below to see a time series plot of the last five days of that observation.

5-day plot - Wind Direction Wind Direction (WDIR):SSW ( 210 deg true )
5-day plot - Wind Speed Wind Speed (WSPD): 1.9 kts
5-day plot - Wind Gust Wind Gust (GST): 1.9 kts
5-day plot - Atmospheric Pressure Atmospheric Pressure (PRES):29.94 in
5-day plot - Air Temperature Air Temperature (ATMP): 77.0 °F
5-day plot - Water Temperature Water Temperature (WTMP): 77.0 °F
5-day plot - Dew Point Dew Point (DEWP): 73.6 °F
5-day plot - Wind Speed at 10 Meters Wind Speed at 10 meters (WSPD10M): 1.9 kts
5-day plot - Wind Speed at 20 Meters Wind Speed at 20 meters (WSPD20M): 1.9 kts
5-day plot -  Wind Speed, Wind Gust and Atmospheric Pressure Combined plot of Wind Speed, Gust, and Air Pressure
Supplemental Measurements
Highest 1-minute Wind Speed
Time (EDT)5-day plot - 1-Minute Wind Speed WSPD 5-day plot - 1-Minute Wind Direction WDIR
8:33 am 1.9 kts-
Previous observations
TIME
(EDT)
5-day plot - Wind Direction
WDIR
 
5-day plot - Wind Speed
WSPD
kts
5-day plot - Wind Gust
GST
kts
5-day plot - Wave Height
WVHT
ft
5-day plot - Dominant Wave Period
DPD
sec
5-day plot - Average Wave Period
APD
sec
5-day plot - Mean Wave Direction
MWD
 
5-day plot - Atmospheric Pressure
PRES
in
5-day plot - Pressure Tendency
PTDY
in
5-day plot - Air Temperature
ATMP
°F
5-day plot - Water Temperature
WTMP
°F
5-day plot - Dew Point
DEWP
°F
5-day plot - Salinity
SAL
psu
5-day plot - Visibility
VIS
nmi
5-day plot - Tide (above MLLW)
TIDE
ft
2024-05-24 08:30 am S 1.9 3.9----29.94- 76.6 76.8 73.6---
2024-05-24 08:20 am S 1.9 3.9 2.0 85.4ENE29.93- 76.8 76.8 73.8---
2024-05-24 08:10 am S 1.9 3.9----29.93- 76.8 76.8 73.6---
2024-05-24 08:00 am S 1.9 3.9----29.93+0.01 76.8 76.8 73.8---
2024-05-24 07:50 am S 1.9 3.9 1.6 75.4 E29.93- 76.8 76.8 73.8---
2024-05-24 07:40 am S 1.9 1.9----29.93- 77.0 77.0 74.1---
2024-05-24 07:30 am S 1.9 3.9----29.93- 76.6 76.8 73.8---
2024-05-24 07:20 amSSE 3.9 3.9 2.0 75.3 E29.93- 76.6 76.8 73.9---
2024-05-24 07:10 amSSE 3.9 3.9 2.0-5.3 E29.92- 76.3 76.8 73.4---
2024-05-24 07:00 am S 1.9 3.9----29.92+0.01 76.1 76.8 73.6---
2024-05-24 06:50 am S 1.9 3.9 2.0 85.7ENE29.92- 75.9 76.8 73.6---
2024-05-24 06:40 am S 1.9 3.9----29.92- 75.7 76.8 73.4---
2024-05-24 06:30 am S 1.9 3.9----29.92- 75.6 76.8 73.2---
2024-05-24 06:20 am S 1.9 3.9 2.0 85.6ENE29.92- 75.6 76.8 73.6---
2024-05-24 06:10 am S 3.9 5.8 2.0-5.6ENE29.92- 75.6 76.8 73.4---
2024-05-24 06:00 am S 3.9 5.8----29.91+0.00 75.4 76.8 73.0---
2024-05-24 05:50 am S 3.9 5.8 2.0 75.6 E29.92- 75.6 76.8 73.4---
2024-05-24 05:40 am S 5.8 5.8----29.91- 75.6 76.8 73.6---
2024-05-24 05:30 am S 5.8 5.8----29.92- 75.6 76.8 73.4---
2024-05-24 05:20 am S 5.8 7.8 2.0 95.6 E29.92- 75.4 76.8 73.2---
2024-05-24 05:10 am S 5.8 7.8 2.0-5.6 E29.92- 75.4 76.8 73.4---
2024-05-24 05:00 am S 3.9 5.8----29.92-0.02 75.6 76.8 73.6---
2024-05-24 04:50 am S 3.9 5.8 2.0 85.7 E29.92- 75.6 77.0 73.6---
2024-05-24 04:40 am S 5.8 7.8----29.91- 75.6 77.0 73.6---
2024-05-24 04:30 am S 5.8 7.8----29.91- 75.6 77.0 73.6---
2024-05-24 04:20 amSSE 5.8 7.8 2.0 85.6 E29.91- 75.6 77.0 73.6---
2024-05-24 04:10 amSSE 5.8 5.8 2.0-5.6 E29.91- 75.6 77.0 73.6---
2024-05-24 04:00 amSSE 5.8 9.7----29.91-0.04 75.6 77.0 73.6---
2024-05-24 03:50 am SE 7.8 9.7 2.0 85.7ENE29.91- 75.6 77.0 73.6---
2024-05-24 03:40 amSSE 7.8 9.7----29.91- 75.6 77.0 73.6---
2024-05-24 03:30 am SE 7.8 9.7----29.91- 75.6 77.0 73.6---
2024-05-24 03:20 am SE 7.8 9.7 2.0 85.8ENE29.91- 75.6 77.0 73.6---
2024-05-24 03:10 am SE 7.8 7.8 2.0-5.8ENE29.92- 75.6 77.0 73.6---
2024-05-24 03:00 am SE 5.8 7.8----29.92-0.04 75.6 77.0 73.6---
2024-05-24 02:50 am SE 3.9 5.8 2.0 85.7 E29.92- 75.6 77.0 73.4---
2024-05-24 02:40 am SE 3.9 3.9----29.93- 75.6 77.0 73.2---
2024-05-24 02:30 amSSE 3.9 5.8----29.93- 75.6 77.0 73.4---
2024-05-24 02:20 amSSE 3.9 5.8 2.0 95.6ENE29.93- 75.7 77.0 73.6---
2024-05-24 02:10 am SE 3.9 5.8 2.0-5.6ENE29.93- 75.7 77.0 73.6---
2024-05-24 02:00 am SE 5.8 5.8----29.94-0.04 75.7 77.0 73.6---
2024-05-24 01:50 am SE 5.8 5.8 2.0 85.6ENE29.94- 75.7 77.0 73.6---
2024-05-24 01:40 am SE 3.9 5.8----29.94- 75.7 77.0 73.6---
2024-05-24 01:30 am SE 3.9 7.8----29.94- 75.7 77.2 73.6---
2024-05-24 01:20 am SE 5.8 7.8 2.0 95.7 E29.94- 75.7 77.2 73.6---
2024-05-24 01:10 am SE 5.8 7.8 2.0-5.7 E29.95- 75.7 77.2 73.8---
2024-05-24 01:00 am SE 5.8 7.8----29.95-0.03 75.9 77.2 73.9---
2024-05-24 12:50 am SE 5.8 7.8 2.0 85.6 E29.96- 75.9 77.2 73.8---
2024-05-24 12:40 am SE 5.8 7.8----29.96- 75.9 77.2 73.8---
2024-05-24 12:30 amSSE 5.8 7.8----29.96- 76.1 77.2 73.8---
2024-05-24 12:20 am SE 5.8 5.8 2.0 85.4ENE29.96- 75.9 77.0 73.4---
2024-05-24 12:10 am SE 5.8 5.8 2.0-5.4ENE29.96- 75.9 77.0 73.4---
2024-05-24 12:00 am SE 5.8 7.8----29.96+0.01 75.9 77.0 73.4---
2024-05-23 11:50 pmSSE 7.8 7.8 2.0 95.4ENE29.96- 75.9 77.0 73.4---
2024-05-23 11:40 pmSSE 5.8 7.8 2.0-5.4ENE29.96- 75.9 77.0 73.4---
2024-05-23 11:30 pmSSE 5.8 7.8----29.97- 75.9 77.2 73.4---
2024-05-23 11:20 pmSSE 5.8 7.8 2.0 85.3ENE29.97- 76.1 77.2 73.6---
2024-05-23 11:10 pmSSE 5.8 7.8 2.0-5.3ENE29.98- 76.1 77.4 73.6---
2024-05-23 11:00 pm S 3.9 9.7----29.98+0.02 76.1 77.4 73.6---
2024-05-23 10:50 pm NW 1.9 3.9 2.0 85.5 E29.98- 75.9 77.4 73.4---
2024-05-23 10:40 pm NE 1.9 3.9----29.98- 75.9 77.5 73.6---
2024-05-23 10:30 pm NE 1.9 3.9----29.98- 75.9 77.5 73.4---
2024-05-23 10:20 pm E 3.9 3.9 2.0 95.3ENE29.98- 75.9 77.5 73.4---
2024-05-23 10:10 pm E 3.9 5.8 2.0-5.3ENE29.98- 75.9 77.7 73.4---
2024-05-23 10:00 pm E 5.8 7.8----29.98+0.02 75.9 77.7 73.4---
2024-05-23 09:50 pm E 5.8 7.8 2.0 95.4ENE29.97- 75.7 77.7 73.4---
2024-05-23 09:40 pm E 7.8 9.7----29.96- 75.9 77.7 73.4---
2024-05-23 09:30 pm E 5.8 7.8----29.96- 75.9 77.7 73.4---
2024-05-23 09:20 pm E 5.8 7.8 2.3 85.5ENE29.96- 75.7 77.7 73.0---
2024-05-23 09:10 pm E 5.8 7.8 2.3-5.5ENE29.96- 75.9 77.7 73.0---
2024-05-23 09:00 pm E 5.8 7.8----29.95+0.00 75.7 77.7 72.9---
2024-05-23 08:50 pmESE 7.8 7.8 2.3 95.5 NE29.95- 75.9 77.7 72.9---
2024-05-23 08:40 pm E 5.8 7.8----29.96- 75.9 77.7 72.7---
2024-05-23 08:30 pm E 3.9 5.8----29.96- 75.9 77.7 72.5---
2024-05-23 08:20 pm E 3.9 5.8 2.3 95.5ENE29.96- 75.9 77.7 72.5---
2024-05-23 08:10 pm E 3.9 5.8 2.3-5.5ENE29.96- 76.1 77.9 72.7---
2024-05-23 08:00 pmENE 3.9 3.9----29.95+0.00 76.3 77.9 72.7---
2024-05-23 07:50 pmENE 1.9 3.9 2.3 95.5ENE29.96- 76.5 77.9 72.7---
2024-05-23 07:40 pmENE 1.9 1.9----29.96- 76.8 77.9 72.9---
2024-05-23 07:10 pmENE 1.9 3.9 2.3-5.3ENE29.95- 77.4 77.9 73.2---
2024-05-23 07:00 pm E 1.9 3.9----29.96+0.00 77.5 77.9 73.2---
2024-05-23 06:50 pm E 1.9 3.9 2.3 95.4 E29.95- 77.5 77.9 73.0---
2024-05-23 06:40 pm E 1.9 3.9----29.95- 77.5 78.1 73.0---
2024-05-23 06:30 pm E 3.9 3.9----29.95- 77.4 77.9 72.9---
2024-05-23 06:20 pm E 3.9 5.8 2.6 95.6 NE29.95- 77.4 77.9 72.9---
2024-05-23 06:10 pm E 1.9 3.9 2.6-5.6 NE29.95- 77.4 77.9 73.0---
2024-05-23 06:00 pmENE 1.9 3.9----29.95-0.02 77.4 77.9 73.0---
2024-05-23 05:50 pmENE 3.9 3.9 2.3 85.4ENE29.95- 77.5 77.9 73.4---
2024-05-23 05:40 pmENE 1.9 3.9 2.3-5.4ENE29.96- 77.4 77.9 72.9---
2024-05-23 05:30 pm E 1.9 3.9----29.96- 77.4 77.9 72.9---
2024-05-23 05:20 pm E 1.9 5.8 2.6 95.7 NE29.96- 77.0 77.9 72.9---
2024-05-23 05:10 pm E 3.9 5.8 2.6-5.7 NE29.96- 76.8 77.9 72.9---
2024-05-23 05:00 pmESE 3.9 5.8----29.96-0.03 76.8 77.9 73.0---
2024-05-23 04:50 pmESE 3.9 5.8 2.6 85.7ENE29.96- 76.8 77.9 73.0---
2024-05-23 04:40 pmESE 3.9 5.8 2.6-5.7ENE29.96- 76.6 77.9 72.9---
2024-05-23 04:30 pmESE 5.8 7.8----29.95- 76.3 77.9 72.5---
2024-05-23 04:20 pmESE 5.8 7.8 2.3 95.5 NE29.96- 76.3 77.9 72.7---
2024-05-23 04:10 pmESE 5.8 7.8 2.3-5.5 NE29.96- 76.3 77.9 72.9---
2024-05-23 04:00 pmESE 7.8 9.7----29.96-0.04 76.3 78.1 72.9---
2024-05-23 03:50 pmESE 7.8 9.7 2.3 95.6ENE29.96- 76.3 77.9 72.9---
2024-05-23 03:40 pmESE 7.8 9.7----29.96- 76.1 77.9 72.7---
2024-05-23 03:30 pmESE 7.8 9.7----29.97- 76.1 77.9 72.7---
2024-05-23 03:20 pmESE 7.8 7.8 2.6 95.7 NE29.97- 76.1 77.7 72.7---
2024-05-23 03:10 pmESE 7.8 9.7 2.6-5.7 NE29.97- 75.9 77.7 72.5---
2024-05-23 03:00 pmESE 7.8 9.7----29.97-0.04 75.9 77.7 72.5---
2024-05-23 02:50 pmESE 7.8 9.7 2.3 105.3ENE29.98- 75.9 77.7 72.5---
2024-05-23 02:40 pmESE 7.8 9.7----29.98- 75.9 77.7 72.5---
2024-05-23 02:30 pmESE 7.8 9.7----29.99- 75.7 77.4 72.3---
2024-05-23 02:20 pmESE 7.8 9.7 2.3 95.7 E29.99- 75.7 77.7 72.7---
2024-05-23 02:10 pmESE 7.8 9.7 2.3-5.7 E29.99- 75.7 77.5 72.5---
2024-05-23 02:00 pmESE 7.8 9.7----29.99-0.01 75.7 77.7 72.5---
2024-05-23 01:50 pm E 7.8 9.7 2.6 95.7 NE29.99- 75.7 77.5 72.5---
2024-05-23 01:40 pm E 7.8 9.7----29.99- 75.7 77.7 72.3---
2024-05-23 01:30 pm E 7.8 9.7----29.99- 75.6 77.5 72.0---
2024-05-23 01:20 pm E 7.8 9.7 2.6 95.8 NE30.00- 75.6 77.5 72.3---
2024-05-23 01:10 pm E 7.8 9.7 2.6-5.8 NE30.00- 75.7 77.4 72.5---
2024-05-23 01:00 pm E 7.8 9.7----30.00+0.00 75.6 77.5 72.3---
2024-05-23 12:50 pm E 7.8 9.7 2.6 96.0 NE30.00- 75.6 77.5 72.1---
2024-05-23 12:40 pm E 7.8 9.7 2.6-6.0 NE30.01- 75.6 77.4 72.3---
2024-05-23 12:30 pm E 7.8 9.7----30.01- 75.6 77.4 72.3---
2024-05-23 12:20 pm E 7.8 9.7 3.0 95.9 E30.01- 75.6 77.4 72.1---
2024-05-23 12:10 pm E 7.8 9.7 3.0-5.9 E30.01- 75.6 77.2 72.3---
2024-05-23 12:00 pm E 7.8 7.8----30.01+0.00 75.6 77.0 72.1---
2024-05-23 11:50 am E 7.8 9.7 2.6 95.4 NE30.01- 75.4 77.0 72.1---
2024-05-23 11:40 am E 7.8 7.8 2.6-5.4 NE30.01- 75.6 77.0 72.3---
2024-05-23 11:30 am E 7.8 9.7----30.00- 75.4 77.0 72.1---
2024-05-23 11:20 am E 7.8 9.7 3.0 95.7 NE30.00- 75.4 77.0 72.0---
2024-05-23 11:10 am E 7.8 9.7 3.0-5.7 NE30.00- 75.4 77.0 72.1---
2024-05-23 11:00 am E 7.8 9.7----30.00-0.01 75.4 77.0 72.1---
2024-05-23 10:50 am E 7.8 9.7 3.0 95.5 NE30.01- 75.6 76.8 72.3---
2024-05-23 10:40 am E 5.8 7.8----30.01- 75.6 76.8 72.1---
2024-05-23 10:30 am E 7.8 9.7----30.01- 75.6 76.8 72.1---
2024-05-23 10:20 am E 7.8 9.7 3.3 95.8 NE30.00- 75.6 76.8 72.1---
2024-05-23 10:10 am E 7.8 9.7 3.3-5.8 NE30.00- 75.6 76.6 72.1---
2024-05-23 10:00 am E 7.8 9.7----30.01+0.01 75.6 76.6 72.1---
2024-05-23 09:50 amENE 7.8 9.7 3.3 95.8ENE30.01- 75.7 76.6 72.3---
2024-05-23 09:40 amENE 5.8 7.8----30.01- 75.7 76.6 72.0---
2024-05-23 09:30 am E 5.8 7.8----30.01- 75.6 76.5 71.8---
2024-05-23 09:20 am E 5.8 7.8 3.3 95.7NNE30.01- 75.6 76.5 71.8---
2024-05-23 09:10 amENE 5.8 7.8 3.3-5.7NNE30.01- 75.6 76.5 71.8---
2024-05-23 09:00 amENE 5.8 7.8----30.02+0.05 75.4 76.5 71.8---
2024-05-23 08:50 amENE 5.8 7.8 3.0 95.4 NE30.02- 75.4 76.5 72.0---

Detailed Wave Summary
for 41002 as of (8:10 am EDT)
1210 GMT on 05/24/2024:

These wave data are displayed in rounded times.

     

Click on the graph icon in the table below to see a time series plot of the last five days of that observation.

5-day plot - Significant Wave Height Significant Wave Height (WVHT): 2.0 ft
5-day plot - Swell Height Swell Height (SwH): 1.6 ft
5-day plot - Swell Period Swell Period (SwP): 7.7 sec
5-day plot - Swell Direction Swell Direction (SwD):ENE
5-day plot - Wind Wave Height Wind Wave Height (WWH): 0.7 ft
5-day plot - Wind Wave Period Wind Wave Period (WWP): 3.7 sec
5-day plot - Wind Wave Direction Wind Wave Direction (WWD): SE
5-day plot - Average Wave Period Average Wave Period (APD): 5.4 sec
Previous observations
TIME
(EDT)
5-day plot - Wave Height
WVHT
ft
5-day plot - Swell Height
SwH
ft
5-day plot - Swell Period
SwP
sec
5-day plot - Swell Direction
SwD
 
5-day plot - Wind Wave Height
WWH
ft
5-day plot - Wind Wave Period
WWP
sec
5-day plot - Wind Wave Direction
WWD
 
5-day plot - Wave Steepness
STEEPNESS
 
5-day plot - Average Wave Period
APD
sec
2024-05-24 07:40 am 1.6 1.6 6.7 E 0.7 3.6 SE N/A 5.4
2024-05-24 07:10 am 2.0 1.6 6.7 E 0.7 3.8 SE N/A 5.3
2024-05-24 06:40 am 2.0 2.0 8.3ENE 0.7 3.8 SE N/A 5.7
2024-05-24 06:10 am 2.0 1.6 8.3ENE 0.7 3.2 SE N/A 5.6
2024-05-24 05:40 am 2.0 2.0 7.1 E 0.7 3.7 SE N/A 5.6
2024-05-24 05:10 am 2.0 2.0 9.1 E 0.7 3.7 SE N/A 5.6
2024-05-24 04:40 am 2.0 2.0 8.3 E 0.7 4.0 SE N/A 5.7
2024-05-24 04:10 am 2.0 1.6 8.3 E 0.7 3.6 SE N/A 5.6
2024-05-24 03:40 am 2.0 2.0 8.3ENE 0.7 3.8 SE N/A 5.7
2024-05-24 03:10 am 2.0 2.0 8.3ENE 0.7 4.0 ESE N/A 5.8
2024-05-24 02:40 am 2.0 2.0 8.3 E 0.7 3.7 SE N/A 5.7
2024-05-24 02:10 am 2.0 1.6 9.1ENE 0.7 4.0 ESE N/A 5.6
2024-05-24 01:40 am 2.0 2.0 8.3ENE 0.7 3.8 ESE N/A 5.6
2024-05-24 01:10 am 2.0 2.0 9.1 E 0.7 3.8 SE N/A 5.7
2024-05-24 12:40 am 2.0 2.0 8.3 E 0.7 4.0 SE N/A 5.6
2024-05-24 12:10 am 2.0 2.0 8.3ENE 0.7 3.6 ESE N/A 5.4
2024-05-23 11:40 pm 2.0 2.0 9.1ENE 0.7 3.8 SE N/A 5.4
2024-05-23 11:10 pm 2.0 2.0 8.3ENE 0.7 3.2 ESE N/A 5.3
2024-05-23 10:40 pm 2.0 2.0 8.3 E 0.7 4.0 SE N/A 5.5
2024-05-23 10:10 pm 2.0 2.0 9.1ENE 0.7 3.8 ESE N/A 5.3
2024-05-23 09:40 pm 2.0 2.0 9.1ENE 0.7 3.7 E N/A 5.4
2024-05-23 09:10 pm 2.3 2.3 8.3ENE 1.0 3.8 SE N/A 5.5
2024-05-23 08:40 pm 2.3 2.0 9.1 NE 1.0 3.6 E N/A 5.5
2024-05-23 08:10 pm 2.3 2.3 9.1ENE 0.7 3.8 ESE N/A 5.5
2024-05-23 07:40 pm 2.3 2.3 9.1ENE 1.0 3.7 ESE N/A 5.5
2024-05-23 07:10 pm 2.3 2.3 9.1ENE 1.0 4.0 SE N/A 5.3
2024-05-23 06:40 pm 2.3 2.0 9.1 E 1.0 3.6 ESE N/A 5.4
2024-05-23 06:10 pm 2.6 2.3 9.1 NE 1.0 3.8 E N/A 5.6
2024-05-23 05:40 pm 2.3 2.3 8.3ENE 1.0 4.0 ESE N/A 5.4
2024-05-23 05:10 pm 2.6 2.3 9.1 NE 0.7 3.3 E N/A 5.7
2024-05-23 04:40 pm 2.6 2.3 8.3ENE 0.7 3.8 ESE N/A 5.7
2024-05-23 04:10 pm 2.3 2.3 9.1 NE 1.0 3.8 ESE N/A 5.5
2024-05-23 03:40 pm 2.3 2.3 9.1ENE 1.0 3.7 ESE N/A 5.6
2024-05-23 03:10 pm 2.6 2.3 9.1 NE 1.0 3.7 ESE N/A 5.7
2024-05-23 02:40 pm 2.3 2.3 10.0ENE 1.0 2.7 E N/A 5.3
2024-05-23 02:10 pm 2.3 2.3 9.1 E 1.0 4.0 ESE N/A 5.7
2024-05-23 01:40 pm 2.6 2.6 9.1 NE 1.0 3.4 E SWELL 5.7
2024-05-23 01:10 pm 2.6 2.6 9.1 NE 1.0 4.0 ESE SWELL 5.8
2024-05-23 12:40 pm 2.6 2.6 9.1 NE 1.0 3.0 E SWELL 6.0
2024-05-23 12:10 pm 3.0 2.6 9.1 E 1.0 3.8 ESE SWELL 5.9
2024-05-23 11:40 am 2.6 2.6 9.1 NE 1.0 3.8 E SWELL 5.4
2024-05-23 11:10 am 3.0 3.0 9.1 NE 1.0 3.8 ESE SWELL 5.7
2024-05-23 10:40 am 3.0 2.6 9.1 NE 1.0 3.3 E SWELL 5.5
2024-05-23 10:10 am 3.3 3.0 9.1 NE 1.0 3.6 E SWELL 5.8
2024-05-23 09:40 am 3.3 3.0 9.1ENE 1.0 3.8 E SWELL 5.8
2024-05-23 09:10 am 3.3 3.0 9.1NNE 1.0 3.6 E SWELL 5.7

Plot of wave energy versus frequency (and period)