Comments on the proposed revisions to the 1927 Hurricane Season
From the Best Track Supervisory Committee
[Replies to the Committee’s comments are indented and in bold face. – Chris Landsea – June 2010.]
General comments: 1. As noted in an earlier e-mail, the committee has serious concerns with the use of non-core observations to adjust the intensity. A glaring example is with storm #2 (incorrectly identified as #3 in the e-mail) on 8 September, where a 50 kt observation was used to decrease the intensity from 80 kt to 60 kt even though the ship was 40+ n mi from the center. The committee again requests that all observations used to change a HURDAT intensity be accompanied by the best possible estimate of the distance from the center.
[Significant intensity changes that are based upon ship observations will include an estimate of the distance of the ship from the center of the cyclone for best track change recommendations provided from this point onward.]
2. There are several examples of bad editing, with information from one storm being mixed with totally unrelated information from another. These occur in the description of storm #1 on 18 August, the description of storm #2 on 11 September, the description of storm #3 on 29 September, and the description of storm #7 on 30 October. Please correct these.
[These are now corrected.]
3. The December 1927 Monthly Weather Review stated that 3-cup anemometers were to become the Weather Bureau standard on 1 January, 1928. Please make note of this if you haven’t already. Also, there are several instances where surface observations were converted from 4-cup standards to 3-cup standards. While these are probably correct, please re-check them if possible to see if any station started using the 3-cup anemometer early.
[Thank you for this reference regarding the 3-cup anemometer change. We have re-checked the dates of the change to the new anemometer and January 1928 was consistently used by nearly all US Weather Bureau stations.]
Storm #1, 1927:
1. Is the 45 kt observation on 19 August close enough to the center to justify the intensity change? The positions suggest it is about 60 n mi away, which is probably not close enough. In a related note, the summary description for 12Z 19 August mentions a 20 kt decrease when it was actually a 10 kt change.
[Agreed. The original HURDAT will be retained on the 19th.]
2. The summary section discusses the 970 mb peripheral pressure. If the positions involved here are correct, this datum is at least 200 n mi from the center and thus of little value in determining the intensity. The recommendation is to remove this reference. Note: Given the distance from the center, is the pressure correct?
[It is agreed that the observation – provided from the MWR Ocean Gales and Storms table in August 1927 – is erroneous. Moreover, it is not clear whether the pressure, position and/or date/time are incorrect. The observation is now noted within the summary as being suspect and not useful for making alterations in HURDAT.]
3. Is the proposed track change during the extratropical phase supported by observations from Nova Scotia? In a related note, the Monthly Weather Review mentions that this system caused damage in New England and gales on the New York coast. This suggests that it was either very large (see point 2) or perhaps west of the proposed track. Please clarify this.
[After obtaining more observations from the U.S. and reexamining the data, he
track has been adjusted between the original HURDAT and what we had proposed. It is of note that the system caused gales in New York, Massachusetts, and Rhode Island. In fact, the system produced high end tropical storm force winds (58 kt 5 min winds) in Nantucket and it might have caused Category 1 sustained winds in Massachusetts. Impacts in Canada from this system and interpretation of the event by Chris Fogarty of the Canadian Hurricane Center do corroborate making this a landfalling hurricane in Canada.]
4. The committee concurs with the delayed extratropical transition, especially in light of the time of year and the transition location originally given in HURDAT. However, is the large reduction in intensity during the extratropical phase justified by the data?
[Agreed that the data does not support a large reduction in intensity on the 25th and 26th given that the ship and coastal data may not be sampling the most intense portion of the cyclone. Only a minor downward adjustment is now indicated on these dates.]
5. The summary section states that the storm dissipated by 12Z on 26 September. This is inconsistent with both the 26 August description and the Monthly Weather Review description of the cyclone reaching Iceland on 27 September. Please provide a better description of the system’s demise.
[We have revisited the decay portion of this cyclone. The system did indeed last
beyond the 26th and we now show an extratropical cyclone phase through 12Z on the 29th. This is supported by the Historical Weather Map and COADS databases.]
Storm #2, 1927:
1. Since 1 September is being dropped from HURDAT, there needs to be an entry for that date and a discussion of why it is being removed.
[Agreed. Observations suggest that the disturbance that developed into the cyclone was still over West African on the 1st. Genesis is delayed 18 hours until 06 UTC on the 2nd.]
2. The committee does not favor the downgrade from hurricane to tropical storm. As mentioned in the general comments, the 50 kt observation on 8 September is likely too far away to be representative of the central intensity. Please restore the original HURDAT intensities for the period 4-9 September. Also, please remove the statement at the end of the summary section regarding how the proposed decrease in intensity has substantial observational support.
[Based upon the revised track, the 50 kt observation on the 8th is about 45 nm to the northeast of the cyclone, though the position of the system is somewhat uncertain. While it is agreed that the large proposed reduction in intensity on the 8th to the 10th was overstated, there still is enough observational evidence – especially on the 9th and 10th – to bring down the intensity a moderate amount. However, it is agreed to retain the system as a hurricane.]
3. On a related note, the 35-kt observation described on 3 September also appears to be 60+ n mi from the center. Is it possible the actual intensity was higher?
[Agreed. As the observation was on the left side of the cyclone and about 60 nm from the center, the intensity is boosted to 45 kt – a 10 kt increase from that indicated originally in HURDAT.]
4. The track of the cyclone as an extratropical low stops at 18Z 11 September 11. What happened to it? Did it dissipate, get absorbed by another low, or continue? Please add a description of the final demise.
[It is of note that the frontal structures shown in the Historical Weather Maps on the 10th and 11th are not supported by available observations. Instead, the system is now reanalyzed to have remained a tropical cyclone until dissipation after 18 UTC on the 11th.]
Storm #3, 1927:
1. The 60-kt observation at 15Z 28 September suggests the possibility the cyclone reached was a hurricane, as shown in the original HURDAT on 29 September. Is there more information on that ob? Since it appears this ship was close to the center, is there a time series of data that could help determine if it sampled the strongest part of the storm? Are the observations on 29 September close enough to the center to rule out the possibility this was a hurricane?
[There were three observations from this ship – as shown in the excel database. But the 60 kt winds were the most intense recorded. This observation (but with no pressure reported) on the 28th is suggestive that hurricane intensity was obtained a day earlier than originally indicated. However, no observations of hurricane force winds (or equivalent in pressure) were explicitly obtained for this system. Nonetheless, the cyclone is maintained as reaching Category 1 hurricane status given the uncertainty.]
2. The proposed reduction in intensity on 23-24 September appears unjustified given the lack of data. The committee notes the observation of 1005 mb with coincident winds of 20 kt on 24 September which appears to be close to the center (inside the RMW?). If the pressure is correct, this suggests the system was a tropical storm.
[Agreed. The 1005 mb peripheral pressure along with 20 kt winds about 45 nm from the center of the cyclone suggest winds of at least 37 kt from the Brown et al. south of 25N pressure-wind relationship. 40 kt reanalyzed for the intensity at 12 UTC on the 24th – up from 35 kt originally.]
3. In the summary paragraph, “(the 29th only) was when it was being absorbed”, please delete the “was when”.
[Agreed. The wording is corrected.]
Storm #4, 1927:
1. The summary section mentions a 50 kt/998 mb ob on 24 September, while the daily sections show this occurring on 25 September. Please correct this.
2. The committee has issues with the proposed downgrade in the peak intensity, which is based on the interpretation of the 35 kt/971 mb ‘peripheral’ observation on 26 September. This observation appears to be about 45-60 n mi from the center, which if correct would not conclusively rule out a higher intensity. However, the combination of 35-kt winds and 971 mb pressure would be more likely to occur inside the RMW, which would make this a ‘core’ observation. The committee currently favors keeping the peak intensity at major hurricane and asks for this ob to be re-analyzed for its accuracy and relationship to the cyclone center.
[It is agreed that the observation is likely a core measurement and the revised track takes the center of the hurricane ~15-20 nm from the ship at the time [08 UTC] of the observation. The 971 mb pressure measurement likely taken inside the RMW suggests a central pressure of 967 mb, utilizing the ~1 mb for each 10 kt wind increment guideline. A 967 mb central pressure suggests winds of 88 kt from the Brown et al. north of 25N pressure-wind relationship and 91 kt from the intensifying subset. The 967 mb value is added into HURDAT. Winds are reanalyzed to be 90 kt at 06 UTC and 95 kt at 12 UTC on the 26th, which may have been the peak intensity for this system.]
3. The 50 kt/998 mb observation on 25 September also appears to be 45-60 n mi from the center. If this is the case, please use the original HURDAT intensities, as the ob is likely too far from the center to calibrate the intensity.
[Agreed. 80 kt at 06 UTC on the 25th is retained.]
Storm #5, 1927:
1. The 35 kt observation used for the peak intensity on 2 October appears to be over 200 n mi from the center (73W versus the center at 77W). If this is correct, please keep the original HURDAT intensity.
[This observation is problematic. It is the strongest wind observation uncovered on the 2nd, but it may be in error. As plotted, the ENE wind direction looks suspicious, as well as the fact that there are three other observations closer to the TC center which are substantially weaker (15 kt each). It is possible that the observation was incorrectly plotted at 73W and instead was supposed to be at 78W. Such a position would be a better fit for both the wind speed and direction, though it is unfortunate that this observation was not to be found in the COADS database. While the observation likely cannot be correct as shown, it is agreed to retain the 45 kt intensity on the 2nd, as there are numerous 25 kt winds observed in the western (weaker) semicircle of the TC.]
2. Even after the appropriate corrections, the 37-kt winds at Charleston are only 3 kt below the proposed peak intensity. Is there information on the anemometer exposure (marine, inland, or something else)? Can it be determined if the ob was at the RMW? It is noted that the Charleston wind record reports an extreme velocity (a gust?) of 61 kt on 3 October. Is this interpretation correct, and what would that value being using a 3-cup anemometer?
[Unfortunately, the only documentation about this station indicates that the height of the station was 15 m above sea level, but no information about anemometer height or exposure. Additionally, without the corresponding pressure information, it is impossible to know how close the peak winds recorded were to the RMW. The “extreme velocity” of 61 kt is a one minute maximum wind, but this value was not considered reliable due to the noisiness of the instrument and is why the “maximum velocity” (or 5 min wind) is what was generally reported in the Monthly Weather Review. Correcting this value of 61 kt directly to the equivalent from a reliable 3-cup anemometer would give 48 kt. This discussion has now been added into the metadata writeup.]
3. The Charleston station record showed a sea-level pressure of 1008.5 mb 3-4 hours after the strongest winds, and a lower pressure likely occurred at that time. If the station record correctly logged peak conditions, this lower pressure was between 1003-1008 mb, as 1003 mb was the lowest for the month.
[Agreed that the lowest pressure observed in Charleston for this system would have been between 1008 and 1003 mb. This has been added into the metadata writeup.]
4. Are any observations on this system available from Savannah, Georgia or Columbia, South Carolina?
[Savannah’s Original Monthly Records do indicate a peak 5 min wind of 31 kt N at 09Z on the 3rd. Unfortunately, Columbia was a secondary station that did not conduct hourly observations, just the 12Z and 00Z measurements, which did not show any significant features.]
5. The committee currently favors keeping the 50 kt peak intensity.
[Agreed to retain the 50 kt peak intensity as well as 50 kt at landfall in South Carolina.]
6. Dunn and Miller describe this system as “minor”. However, the Monthly Weather Review states it was “seemingly quite severe at the time it crossed the coast”. Can Cary Mock check local sources for additional information to see if a small but powerful core made landfall with Charleston outside the RMW?
[Given the somewhat sparsely populated coast south of Charleston in 1927, it is possible that a stronger inner core in this small tropical cyclone had winds up to minimal hurricane intensity. However, no definitive evidence is available to justify this conclusion and the landfall intensity is retained as a 50 kt tropical storm.]
Storm #6, 1927:
1. Given the description of “moderate intensity causing some damage to crops”, it is possible that it was stronger than 40 kt over Cuba. Is there any additional information available from Perez or in Cuban observations?
[Perez agreed with the conclusion of a minimal tropical storm making landfall in Cuba late on the 18th, as no evidence could be obtained to justify a stronger cyclone. It is possible that the “damage to crops” was also ascribed to rain and flooding impacts, not related to wind intensity.]
Storm #7, 1927:
1. The case for the proposed track revisions on 3-4 November is not conclusive. The HWM for 3 November shows an elongated area of low pressure. The proposed change places the tropical cyclone in the southeastern end of this feature. However, the map shows significant cyclonic vorticity off the North Carolina coast which could be the remains of the tropical cyclone. It is recommended that this period be re-analyzed at a higher temporal resolution (every 6 h) to better determine the storm track and whether a separate low formed to the northwest.
[Additional synoptic analyses were conducted at 00Z November 3rd and 00Z November 4th. Unfortunately, not enough observations are available at 06 and 18Z for meaningful analyses to be done. The new storm track for the 3rd and 4th indicates a substantially different evolution than original HURDAT, with the system farther west on the 3rd and dissipated on the 4th. A complex synoptic pattern developed on the 3rd and 4th. As the tropical cyclone moved northward north of the Bahamas on the 3rd, it weakened as a separate, baroclinic system that impacted New England and Canada (and caused significant flooding in New England) began developing over North Carolina and Virginia. At the same time, a large non-tropical low that formed south of Bermuda with gale force winds (this is now included in the Additional Notes section) was occurring on the 3rd and 4th of November. The reanalysis efforts reconfirms that the pre-existing tropical storm, the baroclinic system that impacted New England/Canada, and the third low south of Bermuda were all separate cyclones. It is analyzed that the tropical cyclone remained in that status until dissipation after 18 UTC on the 3rd, while in the warm section of the developing baroclinic low.]
2. The HWM shows a cold front approaching the tropical cyclone from the west on 3 November, presumably in association with an upper-level trough. A northward track would better fit that synoptic pattern, as well as be more climatological.
[Agreed, see above.]
3. Are there any additional data or reports of impact in Cuba available from Perez? If so, please provide the details.
[Perez agreed with the conclusion of a minimal tropical storm making landfall in Cuba around 12Z on the 31st, as no evidence could be obtained to justify a stronger cyclone.]
Storm #8, 1927:
1. The committee concurs with the addition of this system. The possibility that the system was subtropical during its early stages should be considered and noted in the metadata.
[Agreed, so noted.]
System #1: The committee concurs with leaving the system out of HURDAT.
System #2: The committee concurs with leaving the system out of HURDAT. However, it would like more information on the data distribution while the system was a tropical cyclone. Were there any observations near the center on the eastern side that would preclude the possibility of 35 kt winds? It is noted that the 1004 mb pressure would suggest a system near tropical storm strength under normal circumstances.
[Agreed that this system may have been a tropical storm, but do not have the requisite two independent observations of gale force winds/low pressures in order to add the system into HURDAT.]
Other comments: The Monthly Weather Review indicates several systems that should be investigated to see if they were tropical cyclones, or for possible inclusion in the Additional notes section.
1. The May Monthly Weather Review mentions a broad low in the western Gulf of Mexico from 7-10 May. This is likely a baroclinic system, but should be looked at just in case.
[The area of low pressure in the western Gulf of Mexico is shown by the Historical Weather Maps to be part of a very large, powerful extratropical low centered over the south-central U.S. and northern Mexico. This was not a tropical cyclone.]
2. The June Monthly Weather Review mentions an unusual westward-moving low over the north central Atlantic from 28 June into early July. This system is likely too far north to have developed into a tropical cyclone at that time of year, but should be examined.
[This unusual extratropical system did track westward at high latitudes of the North Atlantic in late June and early July. Detailed examination of the system from the Historical Weather Maps and Monthly Weather Review revealed that it remained a large extratropical low with substantial baroclinicity throughout its lifetime and did not make the transition over to a tropical cyclone.]
3. The September Monthly Weather Review mentions a tropical disturbance that recurved near Bermuda in 11 September, with a track on the monthly track map. One of the attachments in the 1927 folder mentions indications of a “considerable disturbance” near Bermuda that “special precautions” were taken for. A northwestward-moving tornado occurred at Bermuda on 11 September, which is consistent with a system south or west of the island. The HWM show a confusing collection of fronts in the area with no obvious low pressure system. Please analyze this case to determine if a tropical cyclone existed.
[Examination revealed that this system itself was clearly part of a large extratropical cyclone.]
4. The November Monthly Weather Review reported a broad low over the northern Caribbean around 20 November with winds up to Force 7. This is likely not a tropical storm but it should be examined.
[The Historical Weather Map Series shows that a strong cold front reached the Caribbean around the 20th of November and resulted in a large area of moderate east to northeast winds in the northern Caribbean. No closed low existed and the system was not a tropical cyclone.]