Southern hemisphere swells travel on average 7-8 days before reaching western US coastal waters. When a swell is within 4 days of arriving, a better prediction can be made using data from coastal buoys. The ability to determine exact arrival time is much less if the swell is roughly from 180 degrees, because it is outside the range of Buoy 51028 (Christmas Island). In such cases, the forewarning for such swells averages less than 12 hours due to the lack of buoys off Central and South America.
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. Estimate the swell direction based on the storms position relative to San Francisco using the tables in Appendix A. Once the swell begins to hit one of the outer buoys listed below (like 51028), write down the time and period of the first reading. Then select the appropriate table based on the estimated swell direction. Browse over to the period column, select the period of the swell that hit buoy 51028, 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 51028 at 10 AM on Monday from 200 degrees, then that swell should hit San Francisco 87 hours later, or on 1 AM Friday.
Swell Angle: 180 Degrees
Hit Order |
Buoy Number |
Distance from Pillar Point (nmiles)* |
Period
(sec) |
Travel Time
(Hrs) & (Days/Hrs) ** |
Buoy Distance from Pillar Point Travel Line *** |
| |
|
|
|
|
|
1 |
46025
Catalina Is |
240 |
@14 |
11 |
<200 nmiles off focus |
| |
|
|
@17 |
9.1 |
|
| |
|
|
@20 |
7.7 |
|
| |
|
|
@25 |
6.2 |
|
| |
|
|
|
|
|
2 |
46028
Cape San Martin |
105 |
@14 |
4.8 |
<100 nmiles off focus |
| |
|
|
@17 |
4.0 |
|
| |
|
|
@20 |
3.4 |
|
| |
|
|
@25 |
2.7 |
|
Swell Angle: 200 Degrees
Hit Order |
Buoy Number |
Distance from Pillar Point (nmiles)* |
Period
(sec) |
Travel Time
(Hrs) & (Days/Hrs) ** |
Buoy Distance from Pillar Point Travel Line *** |
1 |
51028
Christmas Island |
2700 |
@14 |
124
5/3
|
500 nmiles
WNW of
focus |
| |
|
|
@17 |
102
4/4
|
|
| |
|
|
@20 |
87
3/15
|
|
| |
|
|
@25 |
69
3/21
|
|
| |
|
|
|
|
|
2 |
51002
SW Hawaii |
1450 |
@14 |
67.0
2/20
|
1200 nmiles WNW of focus |
| |
|
|
@17 |
55
2/8
|
|
| |
|
|
@20 |
47
1/23
|
|
| |
|
|
@25 |
37
1/13
|
|
| |
|
|
|
|
|
3 |
46025
Catalina Is |
140 |
@14 |
6.4 |
<200 nmiles off focus |
| |
|
|
@17 |
5.3 |
|
| |
|
|
@20 |
4.5 |
|
| |
|
|
@25 |
3.6 |
|
| |
|
|
|
|
|
4 |
46028
Cape San Martin |
80 |
@14 |
3.7 |
<100 nmiles off focus |
| |
|
|
@17 |
3 |
|
| |
|
|
@20 |
2.6 |
|
| |
|
|
@25 |
2.1 |
|
Swell Angle: 220 Degrees
Hit Order |
Buoy Number |
Distance from Pillar Point (nmiles)* |
Period
(sec) |
Travel Time
(Hrs) & (Days/Hrs) ** |
Buoy Distance from Pillar Point Travel Line *** |
1 |
51028
Christmas Island |
2800 |
@14 |
128
5/9
|
200 nmiles
WNW of focus |
| |
|
|
@17 |
106
4/11
|
|
| |
|
|
@20 |
90
3/18
|
|
| |
|
|
@25 |
72
3
|
|
| |
|
|
|
|
|
2 |
51002
SW Hawaii |
1800 |
@14 |
83
3/11
|
1000 nmiles NW of focus |
| |
|
|
@17 |
68
2/19
|
|
| |
|
|
@20 |
58
2/10
|
|
| |
|
|
@25 |
46
1/22
|
|
| |
|
|
|
|
|
3 |
46025
Catalina Is |
55 |
@14 |
2.6 |
<200 nmiles off focus |
| |
|
|
@17 |
2.1 |
|
| |
|
|
@20 |
1.8 |
|
| |
|
|
@25 |
1.5 |
|
| |
|
|
|
|
|
4 |
46028
Cape San Martin |
55 |
@14 |
2.5 |
<100 nmiles off focus |
| |
|
|
@17 |
2.1 |
|
| |
|
|
@20 |
1.8 |
|
| |
|
|
@25 |
1.5 |
|
APPENDIX A
Estimated Swell Direction Based on Storm Position
(This table also provides another alternative for determining Swell Travel Time)
| Storm Longitude and Description |
Storm Latitude |
Distance from San Francisco
(nmiles) |
Swell Direction
(Degrees) |
Estimated Period
(sec) |
Swell Travel Time
(Hrs) |
Swell Travel Time
(Days/Hrs) |
| |
|
|
|
|
|
|
| Due South of San Francisco |
|
|
|
|
|
|
| 122W |
30S |
4050 |
180 |
@14 |
192 |
8/0 |
| |
|
|
|
@17 |
159 |
6/14 |
| |
|
|
|
@20 |
135 |
5/14 |
| |
45S |
4950 |
180 |
@14 |
236 |
9/9 |
| |
|
|
|
@17 |
194 |
8/2 |
| |
|
|
|
@20 |
165 |
6/22 |
| |
60S |
5850 |
180 |
@14 |
279 |
11/14 |
| |
|
|
|
@17 |
229 |
9/14 |
| |
|
|
|
@20 |
195 |
8/2 |
| Southeast of Tahiti |
|
|
|
|
|
|
| 135W |
30S |
4250 |
192 |
@14 |
202 |
8/10 |
| |
|
|
192 |
@17 |
167 |
6/22 |
| |
|
|
|
@20 |
142 |
5/22 |
| |
45S |
5125 |
188 |
@14 |
244 |
10/5 |
| |
|
|
|
@17 |
201 |
8/10 |
| |
|
|
|
@20 |
171 |
7/2 |
| |
60S |
5950 |
187 |
@14 |
283 |
11/19 |
| |
|
|
|
@17 |
233 |
9/17 |
| |
|
|
|
@20 |
198 |
8/7 |
| Southwest of Tahiti |
|
|
|
|
|
|
| 150W |
30S |
4450 |
203 |
@14 |
212 |
8/19 |
| |
|
|
|
@17 |
175 |
7/7 |
| |
|
|
|
@20 |
148 |
6/5 |
| |
45S |
5300 |
197 |
@14 |
252 |
10/12 |
| |
|
|
|
@17 |
208 |
8/17 |
| |
|
|
|
@20 |
177 |
7/10 |
| |
60S |
6100 |
195 |
@14 |
291 |
12/2 |
| |
|
|
|
@17 |
239 |
10/0 |
| |
|
|
|
@20 |
203 |
8/12 |
| South of Cook Islands |
|
|
|
|
|
|
| 165W |
30S |
4800 |
220 |
@14 |
229 |
9/12 |
| |
|
|
|
@17 |
188 |
7/19 |
| |
|
|
|
@20 |
160 |
6/17 |
| |
45S |
5625 |
214 |
@14 |
268 |
11/5 |
| |
|
|
|
@17 |
221 |
9/5 |
| |
|
|
|
@20 |
188 |
7/19 |
| |
60S |
6300 |
200 |
@14 |
300 |
12/12 |
| |
|
|
|
@17 |
247 |
10/7 |
| |
|
|
|
@20 |
210 |
8/19 |
| Southeast of New Zealand |
|
|
|
|
|
|
| 180W |
30S |
5175 |
237 |
@14 |
247 |
10/7 |
| |
|
|
|
@17 |
203 |
8/12 |
| |
|
|
|
@20 |
173 |
7/5 |
| |
45S |
6000 |
218 |
@14 |
286 |
11/22 |
| |
|
|
|
@17 |
235 |
9/19 |
| |
|
|
|
@20 |
200 |
8/7 |
| |
60S |
6650 |
205 |
@14 |
317 |
13/5 |
| |
|
|
|
@17 |
261 |
10/22 |
| |
|
|
|
@20 |
222 |
9/5 |
| Southwest of New Zealand |
|
|
|
|
|
|
| 165E |
30S |
NA |
NA |
@17 |
NA |
NA |
| |
|
|
|
@20 |
NA |
NA |
| |
45S |
NA |
NA |
@17 |
NA |
NA |
| |
|
|
|
@20 |
NA |
NA |
| |
60S |
6975 |
210 |
@17 |
274 |
11/10 |
| |
|
|
|
@20 |
232 |
9/17 |
| Due south of Tasmania |
|
|
|
|
|
|
| 150E |
30S |
NA |
NA |
@17 |
NA |
NA |
| |
|
|
|
@20 |
NA |
NA |
| |
45S |
NA |
NA |
@17 |
NA |
NA |
| |
|
|
|
@20 |
NA |
NA |
| |
60S |
7300 |
215 |
@17 |
286 |
11/22 |
| |
|
|
|
@20 |
243 |
10/2 |
APPENDIX B
Determining Arrival Times of South Pacific Swells
Distance from North
California |
14 secs
21.84 kts/hr |
17 secs
26.52 kts/hr |
20 secs
31.2 kts/hr |
25 secs
39 kts/hr |
| |
Travel Time
(hrs) |
Travel Time (days) |
Travel Time
(hrs) |
Travel Time (days) |
Travel Time
(hrs) |
Travel Time (days) |
Travel Time
(hrs) |
Travel
Time
(days) |
| 4000 |
183 |
7.6 |
151 |
6.3 |
128 |
5.3 |
103 |
4.3 |
| 4100 |
188 |
7.8 |
155 |
6.4 |
131 |
5.5 |
105 |
4.4 |
| 4200 |
192 |
8.0 |
158 |
6.6 |
135 |
5.6 |
108 |
4.5 |
| 4300 |
197 |
8.2 |
162 |
6.8 |
138 |
5.7 |
110 |
4.6 |
| 4400 |
202 |
8.4 |
166 |
6.9 |
141 |
5.9 |
113 |
4.7 |
| 4500 |
206 |
8.6 |
170 |
7.1 |
144 |
6.0 |
115 |
4.8 |
| 4600 |
211 |
8.8 |
174 |
7.2 |
147 |
6.1 |
118 |
4.9 |
| 4700 |
215 |
9.0 |
177 |
7.4 |
151 |
6.3 |
121 |
5.0 |
| 4800 |
220 |
9.2 |
181 |
7.5 |
154 |
6.4 |
124 |
5.1 |
| 4900 |
224 |
9.3 |
185 |
7.7 |
157 |
6.5 |
126 |
5.2 |
| 5000 |
229 |
9.5 |
189 |
7.9 |
160 |
6.7 |
128 |
5.3 |
| 5100 |
234 |
9.7 |
192 |
8.0 |
164 |
6.8 |
131 |
5.5 |
| 5200 |
238 |
9.9 |
196 |
8.2 |
167 |
6.9 |
133 |
5.6 |
| 5300 |
243 |
10.1 |
200 |
8.3 |
170 |
7.1 |
136 |
5.7 |
| 5400 |
247 |
10.3 |
204 |
8.5 |
173 |
7.2 |
139 |
5.8 |
| 5500 |
252 |
10.5 |
207 |
8.6 |
176 |
7.3 |
141 |
5.9 |
| 5600 |
256 |
10.7 |
211 |
8.8 |
180 |
7.5 |
144 |
6.0 |
| 5700 |
261 |
10.9 |
215 |
9.0 |
183 |
7.6 |
146 |
6.1 |
| 5800 |
266 |
11.1 |
219 |
9.1 |
186 |
7.7 |
149 |
6.2 |
| 5900 |
270 |
11.3 |
223 |
9.3 |
189 |
7.8 |
151 |
6.3 |
| 6000 |
275 |
11.5 |
226 |
9.4 |
192 |
8.0 |
154 |
6.4 |
| 6100 |
279 |
11.6 |
230 |
9.6 |
196 |
8.1 |
156 |
6.5 |
| 6200 |
284 |
11.8 |
234 |
9.7 |
199 |
8.3 |
159 |
6.6 |
| 6300 |
289 |
12.0 |
238 |
9.9 |
202 |
8.4 |
162 |
6.7 |
| 6400 |
293 |
12.2 |
241 |
10.0 |
205 |
8.6 |
164 |
6.8 |
|
