Designed and submitted by Pete Wolf, SOO, NWS Jacksonville FL.
Special Marine Warnings (SMWs) are issued for marine areas where thunderstorms are expected to produce hazardous boating conditions, including winds of at least 35 kts, large hail, and waterspouts. On the image below, let's assume we have a line of thunderstorms over south-central GA into north-central FL at 200 pm EST (thick red line)…moving quickly east at 40kts. The thin red lines on the image indicate the expected location of the leading edge at 230 pm, 300pm, and 330 pm (in real time events, this can be determined using the Distance-Speed tool in AWIPS). Radar indicates that the storms are capable of producing 40-50kt winds, potentially large hail, and very heavy rainfall as they move rapidly eastward. However, environmental conditions suggest the line will encounter weaker instability as it moves eastward…suggesting potential for the line of storms to weaken with time.
QUESTION: At what point would a Special Marine Warning (SMW) and/or Marine Weather Statement (MWS) issuance be best, from the perspective of both the customer and the NWS mission? You make the Call!
A. Issue SMW immediately, to give maximum lead time to mariners, despite potential for storms to weaken before reaching the coast.
B. Issue MWS immediately, highlighting potential, then issue SMW at 230 pm, if line remains as intense, to give enough time for protective action by mariners.
C. Issue MWS immediately, highlighting potential, then issue SMW at 300 pm, if line remains as intense, just before line reaches the coastline.
D. Wait to see if line weakens before 300 pm. If intensity is maintained, issue MWS around 300 pm to indicate potential. If necessary (storms remain intense), then issue SMW at 330pm as line moves offshore.
E. Wait to see if line weakens before moving offshore. If it remains intense as it approaches the coast, issue MWS highlighting potential threat…no SMW needed.
BEST ANSWER: B. (A is also a good answer)
Consider that a sailboat can only make 6-8 kts of speed, it can take over an hour to reach port and secure the vessel. Answers that provide less than an hour of lead time provide most recreational mariners with little option other than to ride out the storm, which can be dangerous for some vessels.
Lets review all of the choices.
Choice A: one can easily argue that this is the best choice given the amount of lead time needed by mariners to take protective action. In an environment that suggests the storms will not weaken before moving offshore, this would be the best answer. The main question is how to respond to environments that suggest potential for weakening before storms reach the coast. Is this the best answer from both a customer and NWS mission viewpoint? In this scenario, it may be worth starting with an MWS to indicate potential, while allowing yourself a little more time to better ascertain the likelihood of the threat reaching the coast.
Choice B: this is the best answer available, given the balance between the desire for accuracy and the needs of the customer. While one might want to wait a little longer to see if the line of storms weakens, mariners need more than 30 minutes of lead time to get to shelter (preferably closer to an hour lead time for smaller craft and craft further offshore). Even preparing the vessel to ride out the storm while offshore takes time.
Choice C: At the line's rate of speed, waiting until 300 pm is likely too late for many marine customers, providing less than 30 minutes before the line moves offshore …thus many mariners would have to ride out the storm.
Choice D: While this option would mean the most accurate warning decision, by this point it provides mariners with no option other than to ride out the storm…a risky proposition for some types of vessels (e.g. small sailboats). Many mariners may not know of the threat until receiving a NWR tone-alerted SMW (or seeing the band of cumulonimbus clouds approach).
Choice E: MWS's likely do not get the same amount of reach to marine customers as SMW's (which are tone alerted on NWR). For threats to life and property over the marine waters, this is not the best option.
This scenario illustrates the delicate balance between the need for the most accurate warnings possible and the need by customers for sufficient lead time to take protective action. Unlike over land, where people can rush to shelter in less than 15 minutes, boaters need a much longer period of time to reach port, secure their vessels, and take shelter from the storms (as well as to prepare vessels to ride out a storm while offshore). Providing at least an hour lead time means that many times, the warned storms will weaken considerably before reaching the marine waters. However, the option of waiting until the last minute provides few options to customers who need early warnings to take protective measures.
BEST ANSWER: B. (A is also a good answer)
Consider that a sailboat can only make 6-8 kts of speed, it can take over an hour to reach port and secure the vessel. Answers that provide less than an hour of lead time provide most recreational mariners with little option other than to ride out the storm, which can be dangerous for some vessels.
Lets review all of the choices.
Choice A: one can easily argue that this is the best choice given the amount of lead time needed by mariners to take protective action. In an environment that suggests the storms will not weaken before moving offshore, this would be the best answer. The main question is how to respond to environments that suggest potential for weakening before storms reach the coast. Is this the best answer from both a customer and NWS mission viewpoint? In this scenario, it may be worth starting with an MWS to indicate potential, while allowing yourself a little more time to better ascertain the likelihood of the threat reaching the coast.
Choice B: this is the best answer available, given the balance between the desire for accuracy and the needs of the customer. While one might want to wait a little longer to see if the line of storms weakens, mariners need more than 30 minutes of lead time to get to shelter (preferably closer to an hour lead time for smaller craft and craft further offshore). Even preparing the vessel to ride out the storm while offshore takes time.
Choice C: At the line's rate of speed, waiting until 300 pm is likely too late for many marine customers, providing less than 30 minutes before the line moves offshore …thus many mariners would have to ride out the storm.
Choice D: While this option would mean the most accurate warning decision, by this point it provides mariners with no option other than to ride out the storm…a risky proposition for some types of vessels (e.g. small sailboats). Many mariners may not know of the threat until receiving a NWR tone-alerted SMW (or seeing the band of cumulonimbus clouds approach).
Choice E: MWS's likely do not get the same amount of reach to marine customers as SMW's (which are tone alerted on NWR). For threats to life and property over the marine waters, this is not the best option.
This scenario illustrates the delicate balance between the need for the most accurate warnings possible and the need by customers for sufficient lead time to take protective action. Unlike over land, where people can rush to shelter in less than 15 minutes, boaters need a much longer period of time to reach port, secure their vessels, and take shelter from the storms (as well as to prepare vessels to ride out a storm while offshore). Providing at least an hour lead time means that many times, the warned storms will weaken considerably before reaching the marine waters. However, the option of waiting until the last minute provides few options to customers who need early warnings to take protective measures.
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