The forecast calls for a “small craft advisory.” Latitude 38 once made the comment that these don’t really mean anything. This is false, but I can understand how one might come to that conclusion.
First, there’s no legal definition of “small craft.” However, this means you.
Secondly, none of the many websites of the National Weather Service offers an explanation specifically applicable to our unique San Francisco Bay conditions. But a phone call or two to the NWS elicited the following thresholds for the three types of small craft advisory for our local waters:
1) A small craft advisory is issued if current or forecast sustained winds are 21-33 knots, or frequent gusts of 21-33 knots lasting more than two hours are predicted.
Outside the Gate:
2) A small craft advisory for hazardous seas is issued if the period of the combined seas measured in seconds is less than or equal to the wave height in feet, except when the wave height is less than 5 feet.
3) A small craft advisory for rough bar conditions is issued if breaking waves and/or combined seas of 10 feet or greater are expected on the San Francisco Bar.
The confusion over this advisory results partly from the difference between our summer conditions and winter conditions. In summer, a daily thermal low in California’s central valley pulls wind from the sea through the path of least resistance, which is the Golden Gate. A venturi effect amplifies the velocity in the “slot,” and from there the wind fans out and its speed diminishes. So in the summer, a sailor in the Oakland Estuary may see 10 mellow knots while a boat near Alcatraz may be well reefed down in 30 knots.
In the winter, however, wind velocity is generated by Pacific weather systems that can have massive fronts of over 1000 miles in length. These sweep over the entire bay and may generate sizable waves, so there will be no place to hide.
Since the NWS makes predictions for the highest wind anywhere within the forecast area on a given day, and does not slice our area any smaller than “San Francisco, San Pablo, Suisun Bay and the West Delta,” you need to know summer from winter patterns to interpret this advisory. In fall and spring, take a closer look at the local weather reports, as winds can be generated by either dynamic.
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BoatUS sent this message to its contact list on Wednesday: “In a move that could simplify and potentially reduce misunderstanding of urgent weather messages used by recreational boaters to make critical boating safety decisions, the National Weather Service (NWS) has proposed renaming ‘Small Craft Advisory’ to ‘Small Craft Warning’.” The NWS requests boaters’ feedback. “Boat Owners Association of The United States (BoatUS) urges boaters to speak up now by taking a NWS survey for recreational boaters at www.surveymonkey.com/r/VZGX6BF. The survey closes May 24, 2020.”
© 2020 Stefan Berlinski
“Every day they go boating, boat owners check the weather and then make the decision to either head out or not,” said BoatUS government affairs manager David Kennedy. “We think the name change will help clarify what this means, leading to a better understanding of the severity of a marine weather forecast, and help give recreational boaters the information they need to make smart choices about boating safely.”
For decades, NWS has used the Watch, Warning and Advisory system to alert users about forecast hazards, but it has recognized this can be confusing. The proposal to rename ‘Small Craft Advisory’ to ‘Small Craft Warning’ is part of a larger effort to reduce the messages to just two terms: Watch and Warning. NOAA also says the name change would better align with all other marine warnings — Gale, Storm, and Hurricane Force Wind — leading to greater understanding by recreational boaters.
Changing from ‘Advisory’ to ‘Warning’ would not change the term’s definition. While there is no precise definition of a ‘small craft’, a ‘Small Craft Advisory’ is issued when sustained wind speeds or frequent gusts have reached 20-33 knots, and/or for seas or waves of 4 feet or more, and/or for waves or seas that are potentially hazardous. The requirements vary slightly by region, and local conditions may also prompt a Small Craft Advisory.
Small Craft Advisories are no strangers to San Francisco Bay. It almost seems as if we get one most days when the winds of summer blow through the Gate.
Before you go out to paddle, always check the forecast. While high winds can mean heaven for someone experienced in downwinders and heavy surf can be heaven for experienced surfers, they can also mean serious trouble if you’re not prepared or experienced enough to handle them.
On the coast of North Carolina, we get a lot of weather advisories and not everyone knows what they are or what they mean. There are many different kinds of weather advisories depending on where you live, including Ashfall Advisories for conditions associated with airborne ash plume from a volcanic eruption, Freezing Spray Advisory for an accumulation of freezing water droplets on a vessel at a rate of less than 2 centimeters (cm) per hour caused by some appropriate combination of cold water, wind, cold air temperature, and vessel movement, and Tsunami warnings. The point is, the more you know about your conditions before you go out for a paddle, the better educated you will be when deciding to go out, and more likely you’ll return in safely.
One last note: always be honest with yourself and aware of your skill level and limitations. Don’t put yourself in situations where you’re in over your head. And a great rule of thumb for any paddler is to always let someone know where and when you’re paddling in case you disappear and if at all possible, paddle with a friend. The buddy system is incredibly helpful when situations arise.
Adapted from the National Weather Service FAQs
from USA Today
A Small Craft Advisory (SCA)
A Small Craft Advisory (SCA): An advisory issued by coastal and Great Lakes Weather Forecast Offices (WFO) for areas included in the Coastal Waters Forecast or Nearshore Marine Forecast (NSH) products.
How small craft advisories are issued depend on where you live.
According to the National Weather Service, “There is no precise definition of a small craft. “Any vessel that may be adversely affected by Small Craft Advisory criteria should be considered a small craft. Other considerations include the experience of the vessel operator, and the type, overall size, and sea worthiness of the vessel.”
Here are the definitions for the following regions:
- Eastern (ME..SC, Lake Erie, Lake Ontario) – Sustained winds or frequent gusts ranging between 25 and 33 knots (except 20 to 25 knots, lower threshold area dependent, to 33 knots for harbors, bays, etc.) and/or seas or waves 5 to 7 feet and greater, area dependent.
- Central (MN..OH) – Sustained winds or frequent gusts (on the Great Lakes) between 22 and 33 knots inclusive, and/or seas or waves greater than 4 feet.
- Southern (GA..TX and Caribbean) – Sustained winds of 20 to 33 knots, and/or forecast seas 7 feet or greater that are expected for more than 2 hours.
- Western (WA..CA) – Sustained winds of 21 to 33 knots, and/or wave heights exceeding 10 feet (or wave steepness values exceeding local thresholds).
- Alaska (AK) – Sustained winds or frequent gusts of 23 to 33 knots. A small craft advisory for rough seas may be issued for sea/wave conditions deemed locally significant, based on user needs, and should be no lower than 8 feet.
- Pacific (HI, Guam, etc) – Sustained winds 25 knots or greater and seas 10 feet or greater; except in Guam and the northern Mariana Islands where it is sustained winds 22 to 33 knots and/or combined seas of 10 feet or greater.
Small Craft Advisory for Hazardous Seas (SCAHS)
According to the NWS, “Small Craft Advisory for Hazardous Seas (SCAHS) is an advisory for wind speeds lower than small craft advisory criteria, yet waves or seas are potentially hazardous due to wave height, wave period, steepness, or swell direction. Thresholds governing the issuance of Small Craft.”
Advisories for Hazardous Seas are also specific to geographic areas:
- Eastern (ME..SC, Lake Erie, Lake Ontario) – Seas or waves 5 to 7 feet and greater, area dependent.
- Central (WI..OH) – Seas or waves greater than 4 feet.
- Southern (GA..TX and Caribbean) – Seas 7 feet or greater that are expected for more than 2 hours.
- Western (WA..CA) – Criteria for wave heights and/or wave steepness are locally defined; refer to Western Region Supplement 12-2003, Marine Weather Services.
- Alaska (AK) – Seas or wave conditions deemed locally significant, based on user needs, and should be no lower than 8 feet.
- Pacific (HI, Guam, etc) – Seas 10 feet or greater.
Small Craft Advisory for Rough Bar (SCARB)
Small Craft Advisory for Rough Bar (SCARB): An advisory for specialized areas near harbor or river entrances known as bars. Waves in or near such bars may be especially hazardous to mariners due to the interaction of swell, tidal and/or river currents in relatively shallow water. Thresholds governing the issuance of Small Craft Advisories for Rough Bar are specific to local geographic areas, and are based upon parameters such as wave steepness, wind speed and direction, and local bathymetry.
Small Craft Advisory for Winds (SCAW): An advisory for wave heights lower than small craft advisory criteria, yet wind speeds are potentially hazardous.
Thresholds governing the issuance of small craft advisories are specific to geographic areas:
- Eastern (ME..SC, Lake Erie, Lake Ontario) – Sustained winds ranging between 25 and 33 knots (except 20 to 25 knots, lower threshold area dependent, to 33 knots for harbors, bays, etc.)
- Central (WI..OH) – Sustained winds or frequent gusts (on the Great Lakes) between 22 and 33 knots inclusive.
- Southern (GA..TX and Caribbean) – Sustained winds of 20 to 33 knots that are expected for more than 2 hours.
- Western (WA..CA) – Sustained winds of 21 to 33 knots.
- Alaska (AK) – Sustained winds or frequent gusts of 23 to 33 knots.
- Pacific (HI, Guam, etc) – Sustained winds 25 knots or greater; except in Guam where it is sustained winds of 22 to 33 knots.
Other terms you should know:
BRISK WIND ADVISORY: A Small Craft Advisory issued for ice-covered waters.
GALE WARNING: A warning of sustained surface winds, or frequent gusts, in the range of 34 knots (39 mph) to 47 knots (54 mph) inclusive, either predicted or occurring, and not directly associated with a tropical cyclone.
STORM WARNING: A warning of sustained surface winds, or frequent gusts, in the range of 48 knots (55 mph) to 63 knots (73 mph) inclusive, either predicted or occurring, and not directly associated with a tropical cyclone.
TROPICAL STORM WARNING: An announcement that tropical storm conditions (sustained winds of 39 to 73 mph) are expected somewhere within the specified coastal area within 36 hours.
HURRICANE FORCE WIND WARNING: A warning for sustained winds, or frequent gusts, of 64 knots (74 mph) or greater, either predicted or occurring, and not directly associated with a tropical cyclone.
HURRICANE WARNING: An announcement that hurricane conditions (sustained winds of 74 mph or higher) are expected somewhere within the specified coastal area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds.
Other Advisories, Watches and Warnings for Marine Areas:
Ashfall Advisory: An advisory issued for conditions associated with airborne ash plume resulting in ongoing deposition at the surface. Ashfall may originate directly from a volcanic eruption, or indirectly by wind suspending the ash.
Coastal/Lakeshore Flood Advisory: Flooding is possible (i.e, over and above normal high tide levels. Coastal/Lakeshore Flood Advisories are issued using the Coastal and Lakeshore Hazard Message (CFW) product.
Coastal/Lakeshore Flood Watch: Flooding with significant impacts is possible. Coastal/Lakeshore Flood Watches are issued using the Coastal and Lakeshore Hazard Message (CFW) product.
Coastal/Lakeshore Flood Warning: Flooding that will pose a serious threat to life and property is occurring, imminent or highly likely. Coastal/Lakeshore Flood Warnings are issued using the Coastal and Lakeshore Hazard Message (CFW) product.
Dense Fog Advisory: An advisory for widespread or localized fog reducing visibilities to regionally or locally defined limitations not to exceed 1 nautical mile.
Dense Smoke Advisory: A marine advisory for widespread or localized smoke reducing visibilities to regionally or locally defined limitations not to exceed 1 nautical mile.
Freezing Spray Advisory: An advisory for an accumulation of freezing water droplets on a vessel at a rate of less than 2 centimeters (cm) per hour caused by some appropriate combination of cold water, wind, cold air temperature, and vessel movement.
Gale Watch: A watch for an increased risk of a gale force wind event for sustained surface winds, or frequent gusts, of 34 knots (39 mph) to 47 knots (54 mph), but its occurrence, location,and/or timing is still uncertain.
Hazardous Seas Warning: A warning for wave heights and/or wave steepness values meeting or exceeding locally defined warning criteria.
Hazardous Seas Watch: A watch for an increased risk of a hazardous seas warning event to meet Hazardous Seas Warning criteria but its occurrence, location, and/or timing is still uncertain.
Heavy Freezing Spray Warning: A warning for an accumulation of freezing water droplets on a vessel at a rate of 2 cm per hour or greater caused by some appropriate combination of cold water, wind, cold air temperature, and vessel movement.
Heavy Freezing Spray Watch: A watch for an increased risk of a heavy freezing spray event to meet Heavy Freezing Spray Warning criteria but its occurrence, location, and/or timing is still uncertain.
High Surf Advisory: . A High Surf Advisory is issued when breaking wave action poses a threat to life and property within the surf zone. High surf criteria varies by region. High Surf Advisories are issued using the Coastal Hazard Message (CFW) product.
High Surf Warning: A High Surf Warning is issued when breaking wave action results in an especially heightened threat to life and property within the surf zone. High surf criteria varies by region. High Surf Warnings are issued using the Coastal and Lakeshore Hazard Message (CFW) product.
Hurricane Force Wind Watch: A watch for an increased risk of a hurricane force wind event for sustained surface winds, or frequent gusts, of 34 knots 64 knots (74 mph) or greater, but its occurrence, location, and/or timing is still uncertain.
Hurricane Watch: An announcement that hurricane conditions (sustained winds of 74 mph or higher) are possible within the specified coastal area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane watch is issued 48 hours in advance of the anticipated onset of tropical-storm-force winds.
Low Water Advisory: An advisory to describe water levels which are significantly below average levels over the Great Lakes, coastal marine zones, and any tidal marine area, waterway, or river inlet within or adjacent to a marine zone that would potentially be impacted by low water conditions creating a hazard to navigation.
Severe Thunderstorm Watch: A watch issued when conditions become favorable for severe thunderstorms to develop and headlined in the Coastal Waters Forecast, the Great Lakes Open Lakes Forecast, and the Nearshore Marine Forecast. Reference NWSI 10-512 for severe thunderstorm watch criteria.
Special Marine Warning (SMW): A warning product issued for potentially hazardous weather conditions usually of short duration (up to 2 hours) producing sustained marine thunderstorm winds or associated gusts of 34 knots or greater; and/or hail 3/4 inch or more in diameter; and/or waterspouts affecting areas included in a Coastal Waters Forecast, a Nearshore Marine Forecast, or an Great Lakes Open Lakes Forecast that is not adequately covered by existing marine warnings. Also used for short duration mesoscale events such as a strong cold front, gravity wave, squall line, etc., lasting less than 2 hours and producing winds or gusts of 34 knots or greater.
Storm Watch: A watch for an increased risk of a storm force wind event for sustained surface winds, or frequent gusts, of 48 knots (55 mph) to 63 knots (73 mph), but its occurrence, location, and/or timing is still uncertain
Tornado Watch: A watch issued when conditions become favorable for tornadoes to develop and headlined in the Coastal Waters Forecast, the Great Lakes Open Lakes Forecast, and the Nearshore Marine Forecast . Reference NWSI 10-512 for tornado watch criteria.
Tropical Storm Watch: An announcement that tropical storm conditions (sustained winds of 39 to 73 mph) are possible within the specified coastal area within 48 hours.
Tsunami Advisory: For international products of the Pacific Tsunami Warning Center (PTWC – Pacific (except Alaska, British Columbia and Western States), Caribbean (except Puerto Rico, Virgin Is.), Indian Ocean): The third highest level of tsunami alert. Advisories are issued to coastal populations within areas not currently in either warning or watch status when a tsunami warning has been issued for another region of the same ocean. An Advisory indicates that an area is either outside the current warning and watch regions or that the tsunami poses no danger to that area. The Center will continue to monitor the event, issuing updates at least hourly. As conditions warrant, the Advisory will either be continued, upgraded to a watch or warning, or ended.
For products of the West Coast/Alaska Tsunami Warning Center (WC/ATWC – Alaska, British Columbia and Western States, Canada, Eastern and Gulf States, Puerto Rico, U.S Virgin Islands), and domestic products of the Pacific Tsunami Warning Center (PTWC – Hawaii):
A tsunami advisory is issued due to the threat of a potential tsunami which may produce strong currents or waves dangerous to those in or near the water. Coastal regions historically prone to damage due to strong currents induced by tsunamis are at the greatest risk. The threat may continue for several hours after the arrival of the initial wave, but significant widespread inundation is not expected for areas under an advisory. Appropriate actions to be taken by local officials may include closing beaches, evacuating harbors and marinas, and the repositioning of ships to deep waters when there is time to safely do so. Advisories are normally updated to continue the advisory, expand/contract affected areas, upgrade to a warning, or cancel the advisory.
Tsunami Watch:
A tsunami watch is issued to alert emergency management officials and the public of an event which may later impact the watch area. The watch area may be upgraded to a warning or advisory – or canceled – based on updated information and analysis. Therefore, emergency management officials and the public should prepare to take action. Watches are normally issued based on seismic information without confirmation that a destructive tsunami is underway. An advance alert to areas that could be impacted by destructive tsunami waves based on seismic information without confirmation that a destructive tsunami is underway
Tsunami Warning:
A tsunami warning is issued when a potential tsunami with significant widespread inundation is imminent or expected. Warnings alert the public that widespread, dangerous coastal flooding accompanied by powerful currents is possible and may continue for several hours after arrival of the initial wave. Warnings also alert emergency management officials to take action for the entire tsunami hazard zone. Appropriate actions to be taken by local officials may include the evacuation of low-lying coastal areas, and the repositioning of ships to deep waters when there is time to safely do so. Warnings may be updated, adjusted geographically, downgraded, or canceled. To provide the earliest possible alert, initial warnings are normally based only on seismic information.