To understand the impact of weather on #coffee, you have to understand the biology of the tree. The coffee tree has 3 primary phases that we are dealing with: the #Blooming Phase, the #CherryGrowth Phase and the #Harvest Phase.
These phases occur at different times of year depending on their location with Northern Hemisphere crops Harvesting around October and Southern Hemisphere crops harvesting around April.
During the Blooming phase, #precipitation is essential as rains will trigger the blossoming and are required to sustain the #flowers. The Cherry growth phase also requires regular precipitation for proper development, but it is not as acutely sensitive to rains as during the blooming phase.
This is also when the #newgrowth first appears on the end of the branch and it will grow into a green extension over the course of the growing season. This "new growth" is born with nodes where the flowers will emerge from.
The final phase is the Harvest phase during which the green coffee cherries develop and ripen and are ready to be harvested. Most #washedcoffee is selectively picked by hand to select only ripe cherries which are sent to a wet mill for processing.
#Naturalcoffees are often stripped from the branch en masse with both ripe and partially ripened cherries. These are then laid out on concrete patios to dry before being sent to storage or for processing in #drymills.
In general, the plant "likes" normal weather. So whatever the typical weather is during the phase is desirable for the plant.
During the Blossoming and Cherry Growth phases the tree is most vulnerable to dryness, and to a lesser extent, to heat. A combination of heat and dryness is the worst combination for the crop at this stage.
Particularly wet, wet-seasons can be beneficial for the plant, as can a period of light heat/dryness stress followed by strong rain.
The opposite is true during the harvest season, a warm, dry Harvest season is best, both for the development of the fruit and also for the best post-harvest processing. Wet harvests are a problem primarily because they can make it difficult to dry washed and natural coffees in the sun, and can foster quality defects like mold. Excessive rain can also cause "dropping", this is where the ripe cherries are knocked off the tree by heavy rainfall and can lead to some loss of crop and quality issues.
Additionally, the aforementioned new growth is vulnerable to both #frost and #drought. This new branch growth is essential to host the flowers for the next season's crop so if it is damaged from frost or stunted from drought there will be a reduced crop the following season. Weakened branches and nodes can recover with proper care, rain and temperature, but if a node is sufficiently damaged it will reach a point of no return.
Vietnam is currently in the Harvest phase and is therefore vulnerable to excessive wetness. Now Vietnam is a high-quantity, low-quality origin so quality damage from wetness is not a huge risk, but we have in the past seen rains that were so excessive that they caused significant crop loss from quality.
Current situation is that we have seen some elevated rainfall over the past 30 days, and the forecast is for above average rainfall in the next 2 weeks. Current long-term forecasts show more normal rains over the next several months. Forecasts that far out are not reliable, but for now there is no need to sound the alarm.
Overall these are not at levels where I would be overly concerned yet, but the risk is elevated from where it was and it needs to be observed for changes.
Colombia has seen excessive rains for a long time now, the 90 day cumulative precipitation is 3 standard deviations above normal climatology. Reports from the field are that there has been extensive crop damage to quantity as well as to quality.
The good news is that the weekly and monthly forecasts are showing a dramatic improvement with drier than average weather predicted through the rest of the harvest season. With any luck this will improve the balance of the harvest and mitigate any additional damage. However, we will need to watch closely if this situation changes.
Finally we come to Brazil where this market has seen dramatic damage from frost and prolonged drought. The frost has caused severe damage to the new growth, and for much of this crop there will be no coming back from what was lost. This is on top of reduced new growth from drought and a delayed start to the country's wet season.
The good news is that the rains came in full force in October and completely reversed the terrible fortune for the Brazilian crop. The rain will not undo production that was lost, but they have helped to avert a complete catastrophe to the next season's crop.
Going forward, the weather factor that we will be looking out for will be an early termination to the wet season.