Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 23:47 UTC on 07 August 2014 (above) showed Category 1 Hurricane Iselle just east of Hawai’i, exhibiting a convective burst within the northern semicircle and cloud-top IR brightness temperatures as cold as -82º C. With the approach of Iselle, the Central Pacific Hurricane Center issued its first Hurricane Warning for a portion of Hawai’i since 1993.

An animation of GOES-15 0.63 µm visible channel images during daylight and 10.7 µm IR images at night (below; click to play animation; also available as an MP4 movie file) revealed a deteriorating satellite signature as the hurricane approached the Big Island of Hawai’i — and Iselle was downgraded to a Tropical Storm around 08 UTC on 08 August. However, abundant moisture and orographic effects led to some locations receiving over 10 inches of rainfall in a 24-hour period. In fact, one final convective burst could be seen developing after about 11:00 UTC, moving over the southeastern portion of the Big Island after about 12:45 UTC.

The period of deteriorating satellite signature and weakening intensification were due to the storm encountering increasing deep layer wind shear (below).

View only this post Read Less

GOES-15 visible imagery from after sunrise on 7 August 2014 shows the approach of Pacific Hurricane Iselle towards the ‘Big Island’ of Hawai’i. Orographically-forced clouds are apparent on the northern shores of the entire Island chain, and significant rains are possible as the storm passes — Flash Flood Watches are up for the entire state until 6 AM (HST) Saturday.

There are products available to assess how much rain could potentially fall. For example, the Orographic Rain Index (ORI) uses Total Precipitable Water, 850-mb winds from the Global Forecasting System (GFS) Model and high-resolution topography to determine how much rain might occur if winds are orthogonal (or nearly so) to topography. A real-time display of the product is here.

The moisture environment surrounding Iselle appears to be less hostile today. The water vapor imagery from 1200 UTC, 6 August, showed significant dry air between the storm and Hawaii. That dry air is not so pronounced today (above). Both images cover the same domain and use the same enhancement. Hurricane Julio is apparent in the eastern part of the image from 7 August, above; that storm is forecast to remain north of the island chain.

GOES-15 Infrared Channel (10.7 µm) imagery from 7 August shows periodic deep convection forming in the northern half of Iselle’s circulation, north of an eye-like structure in the infrared. The plot of overshooting tops around Iselle (here) shows that overshoots are being detected again after a relatively quiescent period yesterday and the day before.

Microwave data can be used to measure the intensity of precipitation in/around a tropical cyclone, and the MIMIC-TC pages show animations for active storms. The animation above shows Iselle’s slow weakening — as measured by the intensity of the precipitation in the eyewall.

View only this post Read Less

Hurricanes Iselle and Julio in the central and eastern Pacific Ocean, respectively, are forecast to affect the Hawaiian Islands in the coming days. The True-Color image of Iselle, above, derived from data from Suomi NPP downloaded at NOAA’s X/L Antenna in Hawaii from 2245 UTC on 5 August shows asymmetries in the storm that testify to the presence of dry air ahead of the storm that is wrapping into the circulation from the southwest. (Compare the storm’s presentation at 2245 UTC 5 August, above, to the more circular one 24 hours earlier, at 2300 UTC on 4 August (from this post), when dry air was not impinging on Iselle’s side). The toggle below, between the 11.35 µm imagery, at 1113 UTC and the Day Night Band at the same time shows the ragged appearance of the storm. Coldest cloud tops were -63 C.

GOES-15 water vapor imagery, below, shows the region of dry air in between Iselle and the Hawaiian Islands. Such warm values (the yellow in the enhancement) in the water vapor channel mean the top of the moist layer is low in the troposphere. Of course, water vapor imagery does not quantify the amount of moisture in the atmosphere, it only identifies where the top of the moist layer is. Total Precipitable Water (TPW) can be estimated, with accuracy, using microwave imagery, and the MIMIC TPW for the 72 hours ending at 1100 UTC on 6 August (from this site), below, shows very dry air in advance of the Iselle. Further Information and advisories on Iselle can be found at the website of the Central Pacific Hurricane Center in Honolulu (Link).

Hurricane Julio is also obvious in the TPW animation above, following close on the heels of Iselle. Julio will not have as much dry air to deal with, compared to Iselle, as it moves west-northwestward. However, Julio will move farther north than Iselle, and the cooler water under Julio’s projected track (and somewhat stronger shear) should limit its strength as it moves north of the Hawaiian Islands. (Click here the forecast track for Julio valid 6 August 2014; Click here for the forecast track for Iselle).

Visible imagery from GOES-15, above, at 00 UTC on 6 August, shows that Julio (at that time still a tropical storm) is circular in appearance and lacking an identifiable eye. A burst of convection is apparent over the center, however. The infrared imagery from 00 UTC and 12 UTC, below, shows little change in Julio. It nevertheless strengthened to become the fifth hurricane of the eastern Pacific season.

The toggle above of the 10.7 µm imagery shows an obvious overshooting top at 1200 UTC. Overshooting tops have been correlated with storm intensification. The plot below shows where overshooting tops were identified at 1330 UTC on 6 August (taken from this site). Plots showing the number of overshooting tops as a function of time are available for Iselle and Julio.

View only this post Read Less

As happened in 2011, an algae bloom is ongoing over Lake Erie. The current bloom has contaminated at least one water intake for Toledo, Ohio’s municipal water supply with microcystin, a cyanobacter that when ingested can damage the liver and nauseate people. (There is also significant danger to pets). A series of true-color images (from 4 July, 1 August and 4 August) taken from the MODIS Today website, above, (combining visible channels at 0.6465 µm [red], 0.5537 µm [green] and 0.4656 µm [blue]) shows changes in the water color over the past month. (Image Source: MODIS Today) Some changes are apparent over western Lake Erie that are associated with the toxic bloom.

The algal growth is more readily apparent in the false-color imagery below. This red/green/blue image is constructed with 2.1143 µm imagery as ‘red’, 0.8567 µm imagery as ‘green’ and 0.6465 µm imagery as ‘blue’. The animation including scenes from 4 July, 1 August and 4 August shows dramatic growth between 1 and 4 August. Near-infrared channels — such as 0.8567 µm — are sensitive to energy reflected by algae.

A series of True-Color images for six days this Spring/Summer is here. The increase in algae in the western part of Lake Erie is apparent, but it seems that the outbreak this year is less wide-spread than the outbreak in October of 2011. A series of False-Color images is here.

[Update, 5 August 2014: Toledo’s water supply has been deemed safe to drink]

View only this post Read Less