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These tables help you to establish the swell arrival time on Northern California beaches (relative to San Francisco) providing you know roughly what the swell direction is.   Once the swell begins to hit one of the outer buoys listed below (like 46003), write down the time and period of the first reading.  Then select the appropriate table based on the estimate swell direction, browse over to the period column, select the period of the swell that hit buoy 46003, and browse over to the travel time column that corresponds to that period reading and write that value down.  For exa.cgie, if a 20 second period swell hit 46003 at 10 AM on Monday from 270 degrees, then that swell should hit San Francisco 51.3 hours later, or at 1 PM Wednesday.

Swell Angle: 270 Degrees

Hit Order	Buoy Number	Distance from Pillar Point (nmiles)*	Period (sec)	Travel Time (Hrs)**	Buoy Distance from Pillar Point Travel Line ***
1	46003	1600	@13	78.9	850 nmiles N of focus
			@14	73.3
			@17	60.4
			@20	51.3
			@25	41
2	46006	750	@13	37	300 nmiles N of focus
			@14	34.4
			@17	28.3
			@20	24
			@25	19.2
3	46036	650	@13	32	600 nmiles N of focus
			@14	29.8
			@17	24.5
			@20	20.8
			@25	16.7
4	46002	450	@13	22.2	450 nmiles N of focus
			@14	20.6
			@17	17
			@20	14.4
			@25	11.5
5	46059	380	@13	18.7	150 nmiles N of focus
			@14	17.4
			@17	14.3
			@20	12.2
			@25	9.7
6	46014	71	@13	3.5	Pt Arena
			@14	3.3
			@17	2.7
			@20	2.3
			@25	1.8

 

Swell Angle: 290 Degrees

Hit Order	Buoy Number	Distance from Pillar Point (nmiles)*	Period (sec)	Travel Time (Hrs)**	Buoy Distance from Pillar Point Travel Line ***
1	46003	1700	@13	83.7	200 nmiles N/E of focus
			@14	78
			@17	64.1
			@20	54.5
			@25	43.6
2	46036	850	@13	41.9	350 nmiles N/E of focus
			@14	39
			@17	32.1
			@20	27.2
			@25	21.8
3	46006	730	@13	36	240 nmiles S/W of focus
			@14	33.5
			@17	27.5
			@20	23.4
			@25	18.7
4	46005	700	@13	34.5	290 nmiles N/E of focus
			@14	32.1
			@17	26.4
			@20	22.4
			@25	18
5	46002	525	@13	25.9	0 nmiles off focus
			@14	24.1
			@17	19.8
			@20	16.8
			@25	13.5
6	46059	360	@13	17.7	134 nmiles S/W of focus
			@14	16.5
			@17	13.6
			@20	11.5
			@25	9.2
7	46014	102	@13	5.0	75 nmiles N/E of focus
			@14	4.7
			@17	3.8
			@20	3.3
			@25	2.6

 

Swell Angle: 315 Degrees

Hit Order	Buoy Number	Distance from Pillar Point (nmiles)*	Period (sec)	Travel Time (Hrs)**	Buoy Distance from Pillar Point Travel Line ***
1	46036	900	@13	44.3	0 nmiles off focus
			@14	41.3
			@17	34
			@20	28.9
			@25	23.1
2	46005	680	@13	33.5	75 nmiles N/E of focus
			@14	31.2
			@17	25.7
			@20	21.8
			@25	17.4
3	46006	610	@13	30	468 nmiles S/W of focus
			@14	28
			@17	23
			@20	19.6
			@25	15.6
4	46002	500	@13	24.6	150 nmiles S/W of focus
			@14	23
			@17	18.9
			@20	16
			@25	12.8
5	46059	310	@13	15.3	242 nmiles S/W of focus
			@14	14.2
			@17	11.7
			@20	9.9
			@25	7.9
6	46014	125	@13	6.2
			@14	5.7
			@17	4.7
			@20	4
			@25	3.2

* - Distance corrected for swell angle
** - Travel time is based on distance (corrected for swell angle). For exa.cgie: If a 20 second period swell hits 46006 from 270 degrees, it will take 29 hours for that swell to reach Pillar Point.
*** - This figure provides some indication as to how close the buoy is located to that part of the swell which will eventually strike Pillar Point.

 

APPENDIX A
Swell Profile and Scaling Factors

It is possible to use 'swell measurements' obtained from offshore buoys and convert these measurements to estimate what the swell size will be when it arrives at the San Francisco buoy (46026).

The procedure is:

• Gather necessary meteorological data to ascertain the swell is in-fact traveling towards your locale
• Make mult.cgie readings over time at the selected buoy and develop a swell profile (for that buoy). A swell profile is compiled as in the exa.cgie below (identify the buoy number, date and time the swell was observed, and the actual swell height and period for that time).
• For each reading in the profile, estimate the swell arrival time using tables above.
• Estimate the ‘arriving size’ for each data point in the swell profile. This is acco.cgiished by a.cgiying the appropriate ‘scaling factor’ (see table below) for the a.cgiicable buoy. Si.cgiy mult.cgie the actual swell reading by the appropriate scaling factor below:

Exa.cgie Swell Profile Table

Buoy Number	Date/Time	Comments	Swell Reading	Estimated Arrival Date/Time	Estimated Arrival Size
46006	11/11/97 10:00	Swell Hits	10 ft @ 20 secs
	11/11/97 12:00		12 ft @ 20 secs
	11/11/97 14:00	Swell Maxs	14 ft @ 17 secs
	11/11/97 16:00		13 ft @ 14 secs

 

Scaling Factor Table

OFFSHOREBUOY NUMBER	SWELL ANGLE (degrees)	SCALING FACTOR (for 46014, 46042, 46028, 46063)	SCALING FACTOR (for 46012)
46003	270	.7	.6
	290	.7	.6
	315	NA	NA
46006	270	.8	.6
	290+	.8	.56
	315	.8	.56
46005	All*	.8	.6
46002	All*	.9	.7
46059	270	1.0	.8
	290+	1.0	.75
	315	1.0	.7

* - All swells between 270 and 315 degrees. North of 315 degrees is outside the window for all North CA buoys.

 

Swell Travel Time
This table provides quick-look timings for swells traveling in the NCal Swell window

Distance from North California	11 secs	13 secs	14 secs	17 secs	20 secs	25 secs
600	35	30	28
700	41	35	32
800	47	39	37
900	52	44	41
1000	58	49	46	38
1100	64	54	51	42
1200	70	59	55	45
1300		64	60	49
1400		70	64	53	45
1500		74	69	57	48
1600		79	73	60	51
1700		84	78	64	55
1800		89	83	68	58	46
1900			87	72	61	49
2000			92	76	64	51
2100			96	79	67	54
2200			101	83	71	56
2300			106	87	74	59
2400			110	91	77	62
2500				94	80	64
2600				98	83	67
2700				102	87	69
2800				106	90	72
2900				109	93	74
3000				113	96	77