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USE BUOYS TO PREDICT EXACT SWELL ARRIVAL TIME
FOR SOUTH PACIFIC SWELLS

(Applicable to Central/North California ONLY)

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 example, 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

 

2965

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