GOES-R Satellites (GOES-16 as GOES-East and GOES-18 as GOES-West) provide single-channel observations, such as the clean window infrared image above that can be used to identify features. In the example above, a mid-level cloud deck stretches southeastward from the Samoan islands that surround 170^oW Longitude. Higher clouds with with embedded convection are apparent in the northeastern quadrant of the animation, with a noticeable convective feature forming from 1000 to 1100 UTC. A useful Level 2 product to include in a Clean Window infrared image is the Total Precipitable Water: this is a clear-sky only product and thus gives information where the Band 13 image is returning surface information. The animation below has TPW underlain under the Band 13 image and the default AWIPS enhancement for TPW has been altered: the driest value is 0.5 (inches) rather than 0.0. The TPW distribution allows a viewer to note that the cloud band to the southeast of the Samoan Islands is aligned with a moisture gradient. That deep convective complex is developing near the southern gradient of that deepest moisture. The driest atmosphere is south of 20^oS in the image below.

Derived Motion Wind vectors are another Level 2 product, and they can be plotted as a function of pressure, as shown below. This added information provides useful context to the infrared imagery. At lower levels (surface-900 mb), cloud motion is brisk and from the east and southeast at 20-25 knots. From 775-900 mb, motion is more easterly; derived vectors have appeared on top of the cloud band that stretches southeastward from the Samoan islands. The convection that develops between 1000 and 1100 UTC is within a region of cyclonic winds. Between 600-775 mb, winds are more westerly, and the convection that is developing between 1000 and 1100 UTC is within a region of diffluence associated with anticyclonic motion. Winds from 450-600 mb also show diffluence in the region where convection developed.

The animation below shows the derived winds all plotted on top of each other. AWIPS will also plot vectors such that the wind barb color is a function of wind speed. Low-level winds at this time are mostly derived from the 3.9 µm imagery. High-level winds are derived from Water Vapor channels and from 11.2 µm imagery.

The pronounced shift in wind direction with height is also apparent from the 1200 UTC 17 October 2023 Rawinsonde from Pago Pago, below (from this link).

The persistent winds have raised seas around American Samoa. The buoy at Aunu’u below shows seas climbing to above 10 feet before sunrise American Samoa Time on the 17th. One other recent change that has happened is the cessation of the very long-period southerly swell that had persisted for several days through yesterday.

---

In this environment with persistent winds, Tutuila experienced rain activity that was unforecast by numerical models. Night Microphysics RGB imagery, below, from the CSPP Geosphere site, show the evolution of cloud lines from light violet to violet with a reddish tint as clouds grow in height and start to precipitate.

_______________

Two other GOES-18 Level 2 derived products that helped to further characterize the rain-producing cloud lines were Cloud Top Height (above) and Cloud Top Phase (below). As cloud-top heights increased and reached colder temperatures, their cloud-top phase changed from water (cyan) to supercooled (light green) then to mixed supercooled/ice (darker green). Note that not all of the hourly METAR surface reports were plotted by AWIPS: at 0820 UTC and 0850 UTC, heavy rain reduced the surface visibility to 1.0 and 0.5 mile, respectively, at Pago Pago International Airport on Tutuila Island, American Samoa (plot | text).

Cursor sampling of GOES-18 Cloud Top Phase, Cloud Top Height and Cloud Top Temperature at 1130 UTC — when the maximum height of the cloud line in the vicinity of Tutuila was 22036 ft — is shown below.

View only this post Read Less

MIMIC Total Precipitable Water fields, above, (archived here), show the motion of Typhoon Bolaven as it evolved from a strong typhoon west of 150^o E Longitude on 10 October to a potent extratropical cyclone approaching 150^oW Longitude on 16 October 2023, at which later time a long filament of tropical moisture continued to accompany the system. True Color imagery from the CSPP Geosphere site, below, shows the elongated system with the cold front stretching to the west-southwest.

MIMIC TPW fields over the eastern Pacific at 1800 UTC on 16 October, below, show two different moist airstream; one is affecting the Pacific Northwest of the USA (and southwestern Canada) at 1800 UTC. The moisture with the remains of Bolaven is approaching from the west. The GFS model initialized on 1200 UTC on 16 October suggests the next 72 hours will be wet along Coastal British Columbia with widespread rainfalls of 4-6″ (link, from this site) .

________________

GOES-18 Air Mass RGB images from 14-16 October (above) showed the period during which Typhoon Bolaven made its extratropical transition to a Hurricane Force Low on 14 October and then to an expansive Storm Force Low on 16 October (surface analyses from OPC). The brighter shades of orange-red in the RGB imagery depicted a Potential Vorticity anomaly associated with this strong storm system. 

At 2100 UTC on 16 October, a cross section of AK-NAM40 model Potential Vorticity and Wind Speed along Line J-J’ (below) highlighted a well-defined tropopause fold, descending into the middle troposphere below the core of a 130-140 knot jet stream (the jet axis was situated along the southern periphery of the storm).

---

The storm has generated a particularly large wind field, as shown below (from this website). Between 0650 and 0834 UTC, when Metop-B (twice) overflew the area, the Advanced Scatterometer detected a very large region of 30-35 knot winds (red in the enhancement), with peak winds near 45 knots near 40^oN, 153^oW.

View only this post Read Less

10-minute Full Disk GOES-16 (GOES-East) CIMSS Natural True Color RGB images created using Geo2Grid (above) showed the 2023 Annular Solar Eclipse shadow as it progressed southeastward from the Pacific Northwest to Brazil on 14 October 2023.

GOES-16 Near-Infrared “Vegetation” (0.86 µm) images — in the native projection of the GOES-16 satellite (below) — provided another view of the eclipse shadow path.

A staggered set of three Mesoscale Domain Sectors from GOES-18 (GOES-West) provided 1-minute imagery of the eclipse shadow progression (below).

GOES-16 SUVI Fe171 images from the SSEC Geostationary Satellite Imagery site (below) showed the Moon’s silhouette as it passed in front of the Sun during the eclipse period.

View only this post Read Less

Tropical Storm Sean has developed in the mid-Atlantic and is moving northwest, but is predicted to dissipate by Sunday, 2023-10-15. RealEarth provides an opportunity to look back at the last 48 hours of Sean developing. A video from RealEarth shows GOES-16 true color and Band 13 (10.3 microns, “clean” infrared band) from 2023-10-11 at 1525Z to 2023-10-13 at 1525Z. While signs of convection are apparent on 2023-10-12, the storm structure appears dissipated by the daylight hours of 2023-10-13 when viewing at these wavelengths.

Investigating the finer details of Sean on 2023-10-13, Band 9 (6.95 microns, mid-level water vapor) is examined. A storm structure is hardly noticeable. What stands out in the Atlantic even more in the Band 9 animation is an unnamed disturbance to the East of Sean. (These are the red areas in the Band 9 animation.) The National Hurricane Center predicts this system of having a 10% chance of forming a cyclone in the next 48 hours.

The MIMIC Total Precipitable Water product, below, provides a look back at the last 24 hours of their TPW field. When examining TPW, a more cyclonic structure appears. The TPW field seems to show some actual rotation in Sean, which is harder to notice in the GOES animations.

View only this post Read Less