Hurricane Alex: Heavy rainfall and anomalous precipitable water By Richard H. Grumm National Weather Service Office State College, PA 16803

Transcription

1 Hurricane Alex: Heavy rainfall and anomalous precipitable water By Richard H. Grumm National Weather Service Office State College, PA INTRODUCTION Hurricane Alex ambled across the Gulf of Mexico bringing heavy rainfall to Texas and northern Mexico from 29 June to 2 July 2010 (Fig. 1). A Category 2 storm at landfall; near Soto la Marina, Mexico; Alex was the strongest landfalling hurricane since June The storm center had the second lowest recorded surface pressure in the Atlantic Basin (947 hpa) in the month of June since Hurricane Audrey in June 1957 (946 hpa). The deep cyclone center transported high amounts of moisture into northeastern Mexico and southern Texas. This contributed to heavy rainfall and potentially record high precipitable water values. News reports implied as much as mm (32.26 inches) of rain may have fallen at Estanzuela and 588 mm (23.1 in) at Arroyo Seca 588 mm (23.1) inches of rain fell. The widespread heavy rainfall produced flooding. Flooding was observed in Monterrey, Mexico where a nearby station reported 25 inches of rain during the entire event (Table 1). At Catrina, over 355 mm of rain was observed on 1 July Satellite estimates in Mexico showed storm total precipitation estimates over 500 mm (20 in). Alex caused over 30 deaths. Many of the deaths were in the State of Nuevo Leon where the storm produced heavy rainfall and significant flooding. Monterrey is the Capital of Nuevo Leon. The San Juan and Santa Catarina rivers experienced high water and flooding. The Santa Catarina river is normally a dry river bed but reached record flow during the rainfall associated with Alex. The river flows through Monterrey. The City of Monterrey lies on the eastern edge of the Sierra Madre Oriental Mountains. The higher peaks of the Sierra Madre Oriental reach 3250 to 3300 meters. The data in Figure 1 likely under sampled the rainfall in the mountains of Mexico west of Monterrey. The station shown in Table 1 suggests that higher terrain regions may have had event total rainfall over 750 mm (30 inches). Heavy rainfall was also observed in southern Texas north of the circulation associated with Hurricane Alex. The National Weather Service Office in Corpus Christi, Texas had many observations of rainfall from 2 near 10 inches of rainfall. Flooding closed roads and the NWS had reports of flooding in adjacent areas of Mexico reporting SIGNIFICANT URBAN FLOODING REQUIRED WATER RESCUES ACROSS THE BORDER IN MATAMOROS...TAMAULIPAS MEXICO. AT LEAST 400 NEIGHBORHOODS WERE FLOODED MANY WITH MORE THAN A FOOT OF WATER INTO STRUCTURES. In addition the rainfall, the storm brought high values of precipitable water (PW) into the region. Soundings and model analyses showed over 65mm of

2 PW. At times the PW anomalies were over +5 standard deviations above normal. High PW air and large PW anomalies are often associated with record rainfall events, including land falling tropical systems. This storm was likely a textbook example of this association of heavy rainfall with high PW anomalies. This paper will summarize the pattern and the heavy rainfall associated with Hurricane Alex. The focus is on the patterns and anomalies that produced the heavy rainfall. 2. METHODS The pattern was reconstructed used the NCEP GFS and NAM and were possible the JMA 1.25x1.25 data (Onogi et al. 2007). All data were plotted in GrADS (Doty and Kinter 1995). The severe weather data was overlaid on the JRA data. The higher resolution NCEP NAM is used to show the conditions during the event. The anomalies were computed from the NCEP/NCAR re-analysis data (Kalnay et al 1996) as describe by Hart and Grumm 2001 and Grumm and Hart Unless otherwise stated, the base data was the NAM and the means and standard deviations were computed by comparing the NAM to the NCEP/NCAR 30-year climatological values. For brevity times are referred to in the format of 30/1800 for 30 June UTC and 01/0000 UTC for 01 July 2010 at 0000 UTC. 3. RESULTS i. Large scale pattern Figure 2 shows the large scale pattern over the United States from 28/0000 to 01/1200 UTC. The 500 hpa pattern showed a trough moving into eastern North America and a progressive ridge. The circulation associated with Alex showed up a negative 500 hpa height anomaly moving beneath the strong subtropical ridge (Figs 2d-f). The large scale precipitable water anomalies (Fig. 3) showed a surge of dry air into eastern North America with the trough and a surge of high PW air, with 4 to 5SD positive PW anomalies associated with Alex. Some of this high PW air was clearly moving up the western edge of the subtropical ridge (Fig. 2) toward the end of the period. The deep moisture with Alex came ashore in northern Mexico and southern Texas. ii. Regional pattern The GFS & NAM mean sea level pressure (MSLP) forecasts are shown in Figures 3 & 4. As with most tropical storms and hurricanes, Alex was associated with deep low pressure and -5 to -6 SD pressure anomalies. Both systems showed the surface cyclone center move on shore in Mexico on 1 July The NAM data is in 6-hourly increments and shows the system clearly into Mexico by 01/0600 UTC. The surface system rapidly weakened thereafter. The 850 hpa winds and total wind anomalies are shown in Figure 6. These data show the tight 850 hpa circulation and strong winds. The total wind

3 anomalies were 6SDs above normal just before and during landfall into Mexico (Figs. 6c-f). These strong winds reached close to the slopes of the Sierra Madre Oriental Mountains. These data imply the surge of high moisture was in northern Mexico and southern Texas. The PW and PW anomalies are shown in Figure 7. While the system was offshore, the NAM analyzed over 80mm of PW with 6SD PW anomalies. As the system moved onshore values as high as 72 mm were observed in both northern Mexico and southern Texas. On the initial surge into Mexico, PW values near 80 mm were present at 01/0000 UTC (Fig. 7d). Though not shown, there were very high PW values found in sounding in southern Texas. PW values over 75mm are very rare, this event, with analyzed PW value near 80 mm, clearly had some atypically, if not historic high PW values. Figure 8 shows the 850 hpa moisture flux (MFLUX). Over the Gulf, the high MFLUX values were wrapped about the tight circulation associated with Alex. The first surge of high MFLUX came ashore along the Texas coast by 30/1200 and 30/1800 UTC. The high MFLUX values were generally north of the circulation center. It is possible that the 6SD MFLUX values at 01/0600 UTC are near Monterrey, Mexico (Fig. 8e-f). Clearly, the heavy rainfall was associated with and in close proximity with the high MFLUX values when compared to Figure 1. iii. Rainfall analysis Figure 13 shows the rainfall (Fig. 13) over Texas during the event. Rainfall amounts over Mexico are not present in these data. But heavy rains were close to the values reported by the Corpus Christi, TX office with 128 to 256 mm (5 to 10 inches) of rainfall. iv. Forecasts Figure 14 shows the shorter-range GFS forecasts of rainfall over Texas and Mexico. These forecasts tended to under predict the rainfall in Texas when they covered the same period as shown in Figure 13. Several GFS cycles attempted to predicted 256 or greater rainfall in Mexico, close to where reports of 250 to over 600 mm were observed. The GFS was likely of too coarse a reasolution to predicted the rainfall in the mountains near Monterrey. Nine GEFS QPFs are shown in Figure 15. The ensemble mean is shown here. These data show that the coarser GEFS had lower QPF amounts. However, several members attempted to produce locally heavy rainfall in Mexico in close proximity to where the heaviest rainfall was observed. 4. CONCLUSIONS Hurricane Alex came ashore in coastal Mexico shortly before 0600 UTC 1 July The storm brought strong winds, coastal flooding and heavy rainfall. Additionally, the storm ingested deep tropical moisture which produced extremely high PW values over the western Gulf of Mexico and coastal regions of both Mexico and Texas. The NAM 00-hour analysis of PW (Fig. 7) showed PW value over 80 mm (3.2

4 in) and over 6σ above normal. PW values above 75mm (3 in) are considered very rare. A value of 78.5 mm (3.09 in) was observed in Australia at 1100 UTC 7 December PW values of 72 mm (2.87 in) was observed in the 01/0600 UTC Brownsville, TX sounding (Fig. 9) 2. The 01/1200 UTC sounding fell to 69.8 mm (2.77 in: not shown). Sounding PW values of 69.8 to 73.1 (2.77 to 2.90 in) as far north as Corpus Christi, TX. Rawinsonde climatological data show that record PW values for Corpus Christi, TX are and mm (2.65 and 2.62 in) for June and July respectively (Fig. 11) 3. Clearly, this event had extremely high, if not record high PW values as it came ashore along the Mexican and south Texas coastal zone. The data in Figure 12 suggest that Brownsville, TX may have tied the alltime high PW value at the site with a value of 2.90 inches. More data and information on the rainfall need to be added to this study. But it is clear that this event had near record high PW values and thus produced high MFLUX values and heavy rainfall. The influx of high PW air into the United States and this event may cause some to consider is this the impact of global warming and an increased capacity to hold more water. This may be a potentially interesting avenue of long-term study. More practical matters might be to find events where PW values of 75mm or more have been observed in 1 From the SUNY-Albany Map discussion courtesy of Harald Richter. 2 Courtesy SUNY_Albany Map discussion member Fred Carr. 3 Links/Data Lance Bosart. areas such as the Philippines, Taiwan (Fig. 16), Reunion Island, and other locations were record rains have been observed. The conditions associated with Typhoon Marokot (Fig. 16) show a PW value of 82 mm with a 4 to 5SD PW anomaly at 0000 UTC 7 August These were the highest values found in the JRA in More tropical cases in the Pacific and Indian basins could be examined to see if these events were associated with record rainfall. A potential unique aspect of this event was the high PW air into the mountains of eastern Mexico and some of the unverified heavy rainfall amounts. 5. Acknowledgements Images, links, summaries, and discussions about rawinsondes data were from the SUNY-Albany map list. Lance Bosart, Ed Zisper, Fred Carr, Mike Brennan and Robert Maddox contributed to this dialog and thread. 6. References Doty, B. E., and J. L. Kinter III, 1995: Geophysical data and visualization using GrADS. Visualization Techniques Space and Atmospheric Sciences, E. P. Szuszczewicz and Bredekamp, Eds., NASA, Doty, B. E., and J. L. Kinter III, 1995: Geophysical data and visualization using GrADS. Visualization Techniques Space and Atmospheric Sciences, E. P. Szuszczewicz and Bredekamp, Eds., NASA, Grumm, R.H. and R. Hart. 2001: Standardized Anomalies Applied to Significant Cold Season Weather

5 Events: Preliminary Findings. Wea. and Fore., 16, Hart, R. E., and R. H. Grumm, 2001: Using normalized climatological anomalies to rank synoptic scale events objectively. Mon. Wea. Rev., 129, Junker, N. W., R. H. Grumm, R. Hart, L. F. Bosart, K. M. Bell, and F. J. Pereira, 2008: Use of standardized anomaly fields to anticipate extreme rainfall in the mountains of northern California. Wea. Forecasting,23, Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40- Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77, Onogi, K., J. Tsutsui, H. Koide, M. Sakamoto, S. Kobayashi, H. Hatsushika, T. Matsumoto, N. Yamazaki, H. Kamahori, K. Takahashi, S. Kadokura, K. Wada, K. Kato, R. Oyama, T. Ose, N. Mannoji and R. Taira (2007) : The JRA-25 Reanalysis. J. Meteor. Soc. Japan,85, Lin, Y. and K. E. Mitchell, 2005: The NCEP Stage II/IV hourly precipitation analyses: development and applications. Preprints, 19th Conf. on Hydrology, American Meteorological Society, San Diego, CA, 9-13 January 2005, Paper 1.2.

6 Figure 1. Experimental QPE (in) for the period of 0000 UTC 29 June to 0000 UTC 2 July Courtesy of the National Mosaic & Multi-sensor QPE site.

7 Figure 2. GFS 00-hour forecasts showing 500 hpa heights (m) and anomalies valid at a) 0000 UTC 28 June, b) 1200 UTC 28 June, c) 0000 UTC 29 June, d) 1200 UTC 29 June, e) 0000 UTC 01 July 2010 and f) 1200 UTC 01 July 2010.

8 Figure 3. As in Figure 2 except for precipitable water (mm) and precipitable water anomalies.

9 Figure 4. As in Figure 2 except for GFS 00-hour forecast of mean-sea level pressure (hp) and pressure anomalies.

10 Figure 5. As in Figure 4 except for NAM 00-hour forecasts of valid at a) 0000 UTC 30 June, b) June 210, c) 1800 UTC 30 June 2010, d) 0000 UTC 01 July, e) UTC 01 July, f) 1200 UTC 01 July, g) 1800 UTC 01 July, h) 0000 UTC 02 July, and i) 1200 UTC 02 July

11 Figure 6. As in Figure 5 except for NAM 850 hpa winds and wind anomalies.

12 Figure 7. As in Figure 5 except for precipitable water and precipitable water anomalies.

13 Figure 8. As in Figure 4 except for NAM 850 hpa moisture flux.

14 Figure 9. Broome, Australia Sounding from 1100 UTC 7 December 2007 courtesy of Harald Richter.

15 Figure 10. Brownsville Sounding at 0600 UTC 01 July Links to images came from the SUNY-Albany map group.

16 Figure 11. Corpus Christi sounding climatology for precipitable water (PW) in inches from the Sounding site.

17 Figure 12. As in Figure 11 except for Brownsville, TX.

18 Figure 13. Unified precipitation data rainfall over Texas 28 June to 3 July Return to text.

19 Figure 14. GFS QPF forecasts (mm) for the period ending at 0000 UTC 2 July 2010 from GFS forecasts initialized at a) 0000 UTC 28 June, b) 1200 UTC 28 June, c) 0000 UTC 29 June, d) 1200 UTC 29 June, e) 0000 UTC 01 July and f) 12Z01 July Return to text.

20 Figure 15. As in Figure 14 except for 21-member GEFS forecasts of ensemble mean QPF from forecasts initialized at a) 0600 UTC 27 June, b) 1800 UTC 27 June, c) 0600 UTC 28 June, d) 1200 UTC 28 June, e) 1800 UTC 28 June, f) 0000 UTC 29 June, g) 0600 UTC 29 June, h) 1200 UTC UTC 29 June and i) 1800 UTC 29 June Return to text.

21 Figure 16. JRA25 data showing conditions off the coast of China at 0000 UTC 07 August 2009 data include a) 850 hpa winds and u-wind anomalies, b) 850 hpa winds and v-wind anomalies, c) mean sea level pressure and d) precipitable water (mm) and anomalies.

22 Date Precip (mm) Precip (in) 29-Jun Jun Jul Jul Jul Total: Table 1. Observed rainfall (mm & in) from Catrina near Monterrey Mexico Longitude W latitude 25.68N. Return to introduction.