OPC

Atlantic Mesoscale Oceanic Low in late March 2017

Posted by Michael Folmer on 04/11/2017
Posted in: ABI, G16-CH07_3.9_SWIR, G16-CH08_6.2_WV-Upper-Level, G16-CH09_6.9_WV-Mid-Level, G16-CH10_7.3_WV-Low-Level, OPC, Uncategorized, Water Vapor. Tagged: , , , , . 4 Comments

During the overnight hours of March 19-20, 2017, an amplifying upper level shortwave moved off the Mid Atlantic coast and led to the rapid development of a mesoscale oceanic cyclone across the Gulf Stream east and southeast of Cape Hatteras.  The upper level feature moved south and southeast along the backside of a deep upper level long wave trough near 68W. The global models including the GFS and ECMWF were not well initialized with the upper level shortwave and consistently, over the previous several model runs, were only indicating a weak trough would develop at the surface.  Conversely, the 4km NAM and HRRR were each showing surface low development and significantly higher associated surface winds than shown by the coarser global models.  OPC forecasters had been carrying storm warnings across a few offshore zones through 00 UTC March 20, 2017.

500mb_OPC_analysis

500 mb analysis valid 00 UTC 20 March 2017 issued by the Ocean Prediction Center.  Click here to open in a new window.

NAM_4km_slpwsp_201703

Animation of the 20 March 2017 00 UTC 4 km NAM pmsl and surface winds. Yellow boundaries delineate the OPC offshore forecast zones.  Click here to open in a new window.

The GOES-16 water vapor imagery, including the 6.9 um mid-level and 6.2 um upper-level, suggested that the mid/upper shortwave was more amplified than initialized by the global models.  The feature was also apparent in the GOES-16 7.3 um lower-level water vapor imagery, indicating it may be vertically stacked or at least extend through the lower levels.  The three water vapor channels alone indicated there was likely adequate forcing through the upper and mid levels, and even into the lower levels, to support the development of a surface low.  However, the low level circulation analyzed in the GOES-16 3.9 um shortwave infrared imagery confirmed the presence of the surface low.  In addition, the enhanced baroclinicity the system encountered as it tracked across the Gulf Stream likely played a big role in the storm’s intensification.  The sea surface temperature (SST) gradient along the north wall of the Gulf Stream can be seen in the GOES-16 3.9 um shortwave infrared animation.

G16_6p2_Hatteras_201703

GOES-16 6.2 um upper-level water vapor animation valid 2102 UTC 19 March 2017 – 0902 UTC 20 March 2017.  *Preliminary, Non-Operational Data*  Click here to open in a new window.

G16_6p9_Hatteras_201703

GOES-16 6.9 um mid-level water vapor animation valid 2102 UTC 19 March 2017 – 0902 UTC 20 March 2017.  *Preliminary, Non-Operational Data*  Click here to open in a new window.

G16_7p3_Hatteras_201703

GOES-16 7.3 um lower-level water vapor animation valid 2102 UTC 19 March 2017 – 0902 UTC 20 March 2017.  *Preliminary, Non-Operational Data*  Click here to open in a new window.

G16_3p9_Hatteras_201703

GOES-16 3.9 um shortwave infrared animation valid 2102 UTC 19 March 2017 – 0902 UTC 20 March 2017.  *Preliminary, Non-Operational Data*  Click here to open in a new window.

Upon reviewing the GOES-16 imagery and evaluating the most recent model guidance, the overnight OPC forecaster extended the storm warning through the night period, and also expanded the warning to include the outer mid Atlantic offshore waters. The significantly improved temporal and spatial resolution of the GOES-16 imagery, along with the additional water vapor channels, allowed forecasters to better diagnose the strength of the upper level shortwave and also, the presence of the surface low, which then gave forecasters more confidence in amending the warnings.  Even as the both the upper level feature and the surface low appear to shear and weaken in the three GOES-16 water vapor channels and 3.9 um shortwave infrared band around 06 UTC, there was a ship which reported gale force winds (35 kt) at 06 UTC well southwest of the surface low.

Thanks for reading!

James Clark (OPC) and Michael Folmer (CICS)

“The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.”

 

A Wild Week in the Tropical Pacific (follow-up to 3/11/2015 post)

Posted by Michael Folmer on 03/17/2015
Posted in: MTSAT-2, OPC, Tropical. Tagged: , , , , , , , . Leave a comment

Last week I posted on the very active tropical Pacific Ocean with four storms occurring simultaneously.  Tropical Cyclone Pam (17P) made a devastating visit to the island nation of Vanuatu as a Category 5 (145 kts or 165 mph) cyclone and has since joined the westerlies after passing near New Zealand as a much weaker system.   Currently, the majority of the region has quieted down some, but Tropical Cyclone Nathan (east of Queensland) and Tropical Storm Bavi (West Pacific) are still active, while Tropical Cyclone Olwyn dissipated after making landfall in Western Australia.  Jim Kells (OPC) compiled a few animations that show the evolution of all four tropical cyclones starting on 03/08/15.  The imagery is courtesy of the MTSAT-2 satellite and we are eagerly anticipating the new Himawari-8 satellite data over the next few months.

MTSAT-2 Infrared satellite animation of the four tropical cyclones developing in the tropical Pacific and Indian Oceans valid from 03/08/2015 - 03/16/2015.

MTSAT-2 Infrared satellite animation of the four tropical cyclones developing in the tropical Pacific and Indian Oceans valid from 03/08/2015 – 03/16/2015.

MTSAT-2 Infrared (enhanced) animation similar to the previous animation.

MTSAT-2 Infrared (enhanced) animation similar to the previous animation.

MTSAT-2 Water Vapor animation valid from 03/08/2015 - 03/16/2015.

MTSAT-2 Water Vapor animation valid from 03/08/2015 – 03/16/2015.

So why did it suddenly get so active?

NCEP GEFS forecast of the Madden-Julian Oscillation (MJO).

NCEP GEFS forecast of the Madden-Julian Oscillation (MJO) courtesy of the Climate Prediction Center (CPC).

The MJO is currently near or at a record amplification in Phase 7 and as it swung through Phase 6 to 7, a strong westerly wind burst developed near the equator, while there was enhanced upward motion or ventilation at 200 mb.  This has also been coupled with a sudden drop in the Southern Oscillation Index (another ENSO indicator).

Empirical Wave Propagation forecast for the next 40 days.

Empirical Wave Propagation forecast for the next 40 days courtesy of CPC.

According to one forecast (above), the Empirical Wave Propagation forecast shows a return of favorable tropical cyclone formation conditions (green shading) appearing in the same region from the end of March into early April (the season typically winds down in the Southern Hemisphere after April).

Sea Surface Temperature animation from 12/24/2014 - 03/11/2015 in degrees Celcius.

Sea Surface Temperature animation from 12/24/2014 – 03/11/2015 in degrees Celcius courtesy of CPC.

Sea Surface Temperature Anomaly animation from 12/24/2014 - 03/11/2015.

Sea Surface Temperature Anomaly animation from 12/24/2014 – 03/11/2015 courtesy of CPC.

Finally, notice that this region is where the warmest SSTs reside in the tropical Pacific, along with the strongest warm anomalies.  This is typical of a Modoki El Nino where the warmest conditions are in the Nino 3.4 region or near the Dateline.  Also notice how the water near the coast of South America is colder than normal.  This shows a mixed signal and makes one wonder whether El Nino conditions will be maintained or expand east with time. . .

Thanks for reading!

First Hurricane-Force Low in the East Pacific

Posted by Michael Folmer on 09/30/2014
Posted in: Hurricane-Force Storms, MODIS, OPC, RGB. Leave a comment

From September 20 through September 23, 2014, the Ocean Prediction Center (OPC) was monitoring the development of the season’s first hurricane-force extratropical storm in the East Pacific.  Models were suggesting a marginal hurricane-force wind event would unfold well west of the Pacific Northwest, near 140W longitude, north of 40N latitude.  OPC is routinely using satellite data to monitor and forecast these strong ocean storms.  On this particular event, OPC forecaster James Kells collaborated with Michael Rowland and David Kosier on if and when to pull the trigger on the hurricane-force warning.

GOES-15 6.5 um water vapor animation showing the evolution of the hurricane-force low.

GOES-15 6.5 um water vapor animation showing the evolution of the hurricane-force low.

The above animation shows the evolution of the hurricane-force low, with an eye-like feature evident near the end of the loop.  By 1200 UTC on the 23rd, it was forecast to develop hurricane force winds (64 knots or greater) just west of Oregon near 140W.  During the production of the 1200 UTC OPC Surface Analysis, there was question of whether or not the winds had reached hurricane force intensity. The ASCAT pass from ~0600 UTC showed a large area of 50-55 knot winds in the strong cold advection south of the low center, and the GFS model indicated that the system was still developing.  The GFS 0-30m boundary layer winds also indicated a very small area with hurricane force intensity.

Advanced Scatterometers A and B overlaid on GOES-15 Infrared imagery showing storm force winds at ~0600 UTC on 09/23/14.

Advanced Scatterometers A and B overlaid on GOES-15 Infrared imagery showing storm force winds at ~0600 UTC on 09/23/14.

The 1130 UTC MODIS RGB Air Mass product was timelier, and it showed an area of downward momentum south of the low with the deep purple shading. The corresponding water vapor image was less clear with upper level moisture obscuring the downward motion just beneath it.   In addition, there were no surface reports south of the low center as there were no buoys moored nor drifting in that vicinity.  Furthermore, most ships were aware of the danger and navigated away from the region neglecting the possibility of a surface report in the area of question.

Aqua MODIS RGB Air Mass image from 1130 UTC on 09/23/14.

Aqua MODIS RGB Air Mass image from 1130 UTC on 09/23/14.

A cross-section of the 1200 UTC 09/23/14 GFS model potential temperature and dew point temperature was taken through the low center in order to analyze the depth of the stratospheric intrusion, and also to gauge the magnitude of the downward momentum.  It showed a deep stratospheric intrusion to roughly 500 hPa, and it corroborated the strong downward momentum indicated by the imagery.  The RGB Air Mass image showed the intensity of the downward momentum through the red/purple coloring and gave a good indication of the stronger winds aloft mixing down toward the surface.  The imagery increased confidence with classifying the system as a hurricane force low.

The 1200 UTC 09/23/14 GFS vertical cross-section of potential temperature and dewpoint showing the downward transport of drier air associated with the tropopause fold.

The 1200 UTC 09/23/14 GFS vertical cross-section of potential temperature and dewpoint showing the downward transport of drier air associated with the tropopause fold.

The 1200 UTC 09/23/14 OPC surface analysis.

The 1200 UTC 09/23/14 OPC surface analysis.

For additional images and commentary on this storm, please see the CIMSS Satellite Blog.

~ Guest blogger, James Kells (OPC)