Eastern Pacific Hurricane Rick, shown above near peak intensity at sunset on 17 October 2009, is the second strongest hurricanes on record in the eastern Pacific — weaker only than 1997’s Linda. Sustained winds at this time were estimated to be 180 miles per hour, and the central sea level pressure was estimated to be 906 mb. Note in the visible imagery the presence of gravity waves in the cirrus shield that makes up the central dense overcast (CDO). In addition, as noted in the Tropical Prediction Center discussion issued near this time, the stadium effect in the Hurricane eye is readily apparent.

Rick formed out of a tropical disturbance southwest of the Gulf of Tehuantepec (a loop of 3-hourly water vapor imagery here, and a loop of 6-hourly 11-micron imagery here show an interesting flare-up of convection in the Gulf of Tehuantepec in the days before Rick formed. It is worth pondering how that convection influenced Rick’s early and rapid growth). The evolution from strong tropical depression (here, at 2100 UTC on 15 October) to minimal hurricane (here, at 1500 UTC on 16 October) to category 4 hurricane (here, at 1500 UTC on 17 October to category 5 hurricane, above, was rapid indeed and speaks to the ideal environment through which the disturbance traveled. Consider the image below from the CIMSS Tropical Weather Website.

The image shows that the theoretical minimum to the central pressure in the region through which the system traveled was below 880 mb! (This value is a function of sea surface temperature, and of atmospheric thermodynamic profiles as described here. Note that Rick was moving across ocean waters with surface temperatures close to 30 C as it intensified rapidly. Wind shear as the storm rapidly intensified time was also very low (as diagnosed by Satellite winds). Very warm ocean waters and low vertical wind shear are key ingredients in allowing the strengthening of tropical systems.

The ideal environment resulted in a category 5 storm with a very tall circular ring of convection around the eye. The GOES-11 10.7-micron image, below, shows temperatures of nearly -80 C (the purple pixels within the grey) in the tallest convection around the eye.

(Added: Note in the water vapor and infrared imagery loops, above, the presence of what looks to be a binocular-shaped eye. This is an artifact of the interpolation used to blend GOES-12 and GOES-11 imagery to combine one cohesive picture. In individual images from either satellite, only a single eye is present).

Polar orbiting satellites, such as NOAA-19, give high-resolution images of the storm. The 10.8-micron example above, from 2020 UTC on 17 October, as the storm neared its peak intensity, shows pixels northwest of the storm center (this NOAA-19 pass is ascending, so north is towards the bottom of the image) with brightness temperatures of -84 C. Note also the more circular aspect ratio that comes from the polar-orbiter’s more top-down view, versus the Geostationary satellite’s oblique view. Visible imagery, below, at 0.65 and 0.86 microns, from the NOAA-19 AVHRR instrument, show better storm structure as well.

MODIS imagery from the Terra and Aqua satellites can also be used to investigate the storm. Unfortunately for this storm, the Aqua overpass granule split was right across the storm eye (granules are created so that the vast amount of data created by the satellite are more easily transportable). Gluing the two images together does not re-capture all the missed points, but it does give a good representation of the storm intensity here. A later MODIS image from TERRA, below, from 1755 UTC on 18 October (that is, about a day after the image from Aqua), below, shows a somewhat cloudier, but still quite distinct, eye. At this point, Rick has passed its peak in intensity.

(added: Jesse at Accu-Weather has other imagery of Rick here).

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A cold airmass over the Great Lakes states and northeast that allowed an unprecedentedly early snowfall over central Pennsylvania (see precipitation totals ending at 1200 UTC on 16 October here) is also supporting the development of Lake-effect precipitation downwind of Lake Michigan. In the loop above (click the loop to enlarge), pay attention to the cumuliform cloud development over the relatively warm waters of Lake Michigan, and note how the straight lines of clouds move south-southwestward towards the lake counties of Wisconsin and Illinois. These cumuliform clouds contain showers as noted in the radar imagery here. The plot of surface data (below) at 1800 UTC shows a prevailing northerly or north-northeasterly flow at the surface, consistent with the motion of the lake-effect clouds. Note also the plots from moored buoys over the Lakes (plotted in red) that show temperatures in the low 50s (11-12 Celsius) over Lake Michigan and mid 40s (7-8 Celsius) over cooler Lake Superior.

The 850-hPa temperatures observed by radiosondes over the midwest at 1200 UTC on 16 October (here) show temperatures cooler than -5 Celsius over Lake Michigan. In general, a temperature difference of at least 13 C between 850 hPa and the Lake Surface is looked for when forecasting lake-effect precipitation. Observations in the surface plot certainly support a temperature difference exceeding 13 C between the lake surface and 850 hPa. Estimates of lake surface temperature from satellite have been hampered lately by persistent cloudiness over the Great Lakes basin. An MODIS estimate from 1800 UTC today, however, located here, does show temperatures in the 50s over Lake Michigan, and somewhat cooler waters over Lake Superior. This cooler lake temperatures in Lake Superior may explain in part the lack of lake-effect clouds just downwind of Lake Superior over the eastern part of the upper Peninsula (It is likely that other forcings may be suppressing cloud formation there as well; note that at the beginning of the visible imagery loop, cloud streets do extend from Lake Superior into the upper Penisula of Michigan just to the east of Marquette; these cloud streets dissipate with time, suggesting strong subsidence in the region).

Development of lake-effect clouds in mid-October is a reminder of what is to come in the near future as cooler and cooler airmasses develop over Canada and move southward over the still-warm Great Lakes.

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Snow is widespread today from central Pennsylvania northward into central New York. Accumulating snow only rarely falls this early in the season in that part of the country, and at many stations this is the earliest measurable snow on record. The above image is an enhanced 11-micron image from GOES-12 with surface observations (in white) and buoy observations (in black) superimposed. (Click image to enlarge)

One reason for snow’s rarity can be viewed in the sea surface temperatures plotted in black — ocean surface temperatures are still in the low 60s off the coast of New Jersey. That source of relative warmth can have a powerful effect if the wind is from the east, and it can be fatal to a snowfall.

Much of the moisture from this storm, however, is not coming from the east, but from the west and southwest, as suggested in this plot of total precipitable water — plotted as a percentage of normal — derived from AMSU and SSM/I instruments on the NOAA polar orbiters. (See image here; note the axis of high percentages along the spine of the Appalachians).

A vital feature for the production of snow is the presence of ice crystals within a mixed-phase cloud. When that happens, the Bergeron-Findeisen process allows ice crystals to grow at the expense of water droplets, and these ice crystals can then fall towards the surface, either maintaining their integrity as snow all the way down or melting to rain drops. If ice crystals are not present, cloud droplets will grow via Collision and Coalescence, and a drizzle or light rain is more likely. Cloud types derived from different channels on MODIS (image here, valid at 1534 UTC on 15 October) and from AVHRR (image here, valid at 1721 UTC 15 October). Both images suggest that the presence of ice crystals for the seeder-feeder mechanism might be limited if winds at cloud level are westerly. Should that happen, the snow of this afternoon would become light rain or drizzle tonight. MODIS cloud phase from 1710 UTC of 15 October, however, which has a swath farther to the west, does show more ice clouds upstream of Pennsylvania and New York, an observation that suggests snow may continue, if surface and near-surface temperatures remain cool enough.

(Updated, 16 October: Some snow totals as of 1200 UTC 16 October: 4.7″ in State College, 3.2″ in Philipsburg, 2.4″ in Altoona, 5.9″ in Wellsboro)

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Columbus Day is the Anniversary of a truly historic storm in the Pacific Northwest. On October 12, 1962, one of the most intense storms on record caused wind gusts exceeding hurricane force over a broad swath of coastal Washington and Oregon. Now, 47 years later, a weaker but still potent storm is poised to move onshore.

Water vapor imagery (above) shows the characteristic signal of a strong jet, with a dark band, indicating sinking and drying (and warmer brightness temperatures because the satellite sensor is seeing farther down into the atmosphere), on the poleward side of the strongest winds. Aircraft wind observations (plotted in red) show numerous observations of wind speeds exceeding 150 knots, and the GFS analysis 6-hr forecast valid at 1200 UTC this morning (the time of the water vapor image) shows a 160+ knot jet on the 345 K isentropic surface.

The big storm of 1962 could be easily linked to a tropical cyclone that moved north just west of the Dateline. Is the jet now present in the Pacific linked to Typhoon Melor, which storm was off the coast of Japan last week? This animation of enhanced 11-micron imagery over the Pacific Ocean suggests that it is. Certainly the moisture from the tropical system is part of the jet; careful inspection of the imagery suggests that the mid-level vorticity from Melor is also involved in this jet.

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